Annual report pursuant to Section 13 and 15(d)

Derivative Instruments and Hedging Activities - Effects on statements of income and consolidated statements of comprehensive income (Details)

v3.10.0.1
Derivative Instruments and Hedging Activities - Effects on statements of income and consolidated statements of comprehensive income (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]      
Gain (loss) on derivatives recognized in net income (loss) $ (121) $ (271) $ (279)
Nonoperating Income (Expense) | Designated as Hedging Instrument | Interest Rate Swap      
Derivative Instruments, Gain (Loss) [Line Items]      
Amount of gain (loss) recognized in net income (loss) (196) (271) (279)
Nonoperating Income (Expense) | Not Designated as Hedging Instrument | Interest Rate Swap      
Derivative Instruments, Gain (Loss) [Line Items]      
Gain (loss) on derivatives recognized in net income (loss) (308) 0 0
Nonoperating Income (Expense) | Not Designated as Hedging Instrument | Commodity swap contracts      
Derivative Instruments, Gain (Loss) [Line Items]      
Gain (loss) on derivatives recognized in net income (loss) 36 0 0
Nonoperating Income (Expense) | Not Designated as Hedging Instrument | Hybrid Instrument      
Derivative Instruments, Gain (Loss) [Line Items]      
Gain (loss) on derivatives recognized in net income (loss) $ 337 $ 0 $ 0