Annual report pursuant to Section 13 and 15(d)

Business Segment Information - Segment Information (Details)

v3.10.0.1
Business Segment Information - Segment Information (Details) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Dec. 31, 2018
Sep. 30, 2018
Jun. 30, 2018
Mar. 31, 2018
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Segment Reporting Information [Line Items]                      
Revenues $ 217,371 $ 205,375 $ 196,982 $ 167,410 $ 211,133 $ 204,744 $ 166,665 $ 134,610 $ 787,138 $ 717,152 $ 651,227
Interest income                 282 130 50
Interest income                 15,344 9,082 7,076
Depreciation and intangible asset amortization                 29,148 23,915 22,764
Unallocated corporate activity                 (30,415) (27,195) (32,225)
Income before taxes, excluding unallocated corporate activity                 72,805 55,912 48,592
U.S. Regions                      
Segment Reporting Information [Line Items]                      
Revenues                 334,344    
U.S. Federal                      
Segment Reporting Information [Line Items]                      
Revenues                 246,309    
Non-solar DG                      
Segment Reporting Information [Line Items]                      
Revenues                 82,655    
Operating Segments | U.S. Regions                      
Segment Reporting Information [Line Items]                      
Revenues                 334,344 290,196 276,766
Interest income                 9 2 1
Interest income                 6,188 2,672 1,055
Depreciation and intangible asset amortization                 5,578 2,974 1,901
Income before taxes, excluding unallocated corporate activity                 20,543 13,865 19,802
Operating Segments | U.S. Federal                      
Segment Reporting Information [Line Items]                      
Revenues                 246,309 229,146 178,005
Interest income                 126 44 11
Interest income                 1,045 1,056 942
Depreciation and intangible asset amortization                 2,772 2,623 2,588
Income before taxes, excluding unallocated corporate activity                 36,332 29,261 22,246
Operating Segments | Canada                      
Segment Reporting Information [Line Items]                      
Revenues                 38,982 43,803 50,448
Interest income                 0 1 0
Interest income                 1,917 1,927 1,737
Depreciation and intangible asset amortization                 1,155 1,178 1,090
Income before taxes, excluding unallocated corporate activity                 (2,746) 1,751 (2,330)
Operating Segments | Non-solar DG                      
Segment Reporting Information [Line Items]                      
Revenues                 82,655 79,220 74,395
Interest income                 147 83 38
Interest income                 6,172 3,389 3,319
Depreciation and intangible asset amortization                 18,101 15,259 14,557
Income before taxes, excluding unallocated corporate activity                 13,412 8,115 9,301
Operating Segments | Other                      
Segment Reporting Information [Line Items]                      
Revenues                 84,848 74,787 71,613
Interest income                 0 0 0
Interest income                 22 38 23
Depreciation and intangible asset amortization                 1,542 1,881 2,628
Income before taxes, excluding unallocated corporate activity                 5,264 2,920 (427)
Consolidation, Eliminations                      
Segment Reporting Information [Line Items]                      
Unallocated corporate activity                 (30,415) (27,195) (32,225)
Consolidation, Eliminations | U.S. Regions                      
Segment Reporting Information [Line Items]                      
Unallocated corporate activity                 0 0 0
Consolidation, Eliminations | U.S. Federal                      
Segment Reporting Information [Line Items]                      
Unallocated corporate activity                 0 0 0
Consolidation, Eliminations | Canada                      
Segment Reporting Information [Line Items]                      
Unallocated corporate activity                 0 0 0
Consolidation, Eliminations | Non-solar DG                      
Segment Reporting Information [Line Items]                      
Unallocated corporate activity                 0 0 0
Consolidation, Eliminations | Other                      
Segment Reporting Information [Line Items]                      
Unallocated corporate activity                 $ 0 $ 0 $ 0