Annual report pursuant to Section 13 and 15(d)

Business Segment Information - Segment Information (Details)

v3.8.0.1
Business Segment Information - Segment Information (Details) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Segment Reporting Information [Line Items]                      
Revenues $ 211,133 $ 204,744 $ 166,665 $ 134,610 $ 174,225 $ 180,598 $ 162,628 $ 133,776 $ 717,152 $ 651,227 $ 630,832
Interest income                 130 50 1,331
Interest income                 9,082 7,076 5,250
Depreciation and intangible asset amortization                 23,915 22,764 21,522
Unallocated corporate activity                 27,195 32,225 26,077
Income before taxes, excluding unallocated corporate activity                 55,912 48,592 26,369
Operating Segments | U.S. Regions                      
Segment Reporting Information [Line Items]                      
Revenues                 290,196 276,766 306,086
Interest income                 2 1 1
Interest income                 2,672 1,055 359
Depreciation and intangible asset amortization                 2,974 1,901 1,823
Income before taxes, excluding unallocated corporate activity                 13,865 19,802 25,856
Operating Segments | U.S. Federal                      
Segment Reporting Information [Line Items]                      
Revenues                 229,146 178,005 127,620
Interest income                 44 11 1
Interest income                 1,056 942 0
Depreciation and intangible asset amortization                 2,623 2,588 1,209
Income before taxes, excluding unallocated corporate activity                 29,261 22,246 16,676
Operating Segments | Canada                      
Segment Reporting Information [Line Items]                      
Revenues                 43,803 50,448 49,235
Interest income                 1 0 1,154
Interest income                 1,927 1,737 1,338
Depreciation and intangible asset amortization                 1,178 1,090 1,081
Income before taxes, excluding unallocated corporate activity                 1,751 (2,330) (15,449)
Operating Segments | Non-solar DG                      
Segment Reporting Information [Line Items]                      
Revenues                 79,220 74,395 61,626
Interest income                 83 38 175
Interest income                 3,389 3,319 3,553
Depreciation and intangible asset amortization                 15,259 14,557 13,331
Income before taxes, excluding unallocated corporate activity                 8,115 9,301 7,609
Operating Segments | Other                      
Segment Reporting Information [Line Items]                      
Revenues                 74,787 71,613 86,265
Interest income                 0 0 0
Interest income                 38 23 0
Depreciation and intangible asset amortization                 1,881 2,628 4,078
Income before taxes, excluding unallocated corporate activity                 2,920 (427) (8,323)
Consolidation, Eliminations                      
Segment Reporting Information [Line Items]                      
Unallocated corporate activity                 (27,195) (32,225) (26,077)
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