Other Comprehensive Income (Loss) - Accumulated other comprehensive income (loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss)
Accumulated other comprehensive income (loss), balance at beginning of period, net	$ 781	$ 61,981
Foreign currency translation adjustments	1,027
Other comprehensive income (loss) before reclassifications	6,146	1,939
Amounts reclassified from accumulated other comprehensive income (loss)	(7,072)	(63,139)
Accumulated other comprehensive income (loss), balance at end of period, net	882	781
Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss)
Foreign currency translation adjustments	1,027
Accumulated other comprehensive income (loss), balance at end of period, net	1,027
Unrealized/Recognized Gains (Losses)
Accumulated Other Comprehensive Income (Loss)
Accumulated other comprehensive income (loss), balance at beginning of period, net	781	61,981
Other comprehensive income (loss) before reclassifications	6,146	1,939
Amounts reclassified from accumulated other comprehensive income (loss)	(7,072)	(63,139)
Accumulated other comprehensive income (loss), balance at end of period, net	$ (145)	$ 781