Other Comprehensive Income (Loss) - Other comprehensive income (loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other comprehensive income (loss), before tax amount
Other comprehensive income (loss), before tax amount	$ (1,880)	$ (431)	$ (96,262)
Other comprehensive income (loss), tax (expense) benefit
Other comprehensive income (loss), tax (expense) benefit	124	532	35,062
Other comprehensive income (loss):
Total other comprehensive income (loss), net of tax	(1,756)	101	(61,200)
Foreign Currency Translation Adjustment
Other comprehensive income (loss), before tax amount
Other comprehensive income (loss), before reclassifications, before tax	(1,343)	1,027
Other comprehensive income (loss):
Other comprehensive income (loss), before reclassifications, net of tax	(1,343)	1,027
Unrealized/Recognized Gains (Losses)
Other comprehensive income (loss), before tax amount
Other comprehensive income (loss), before reclassifications, before tax	(529)	9,671	3,050
Amounts reclassified from accumulated other comprehensive income (loss), before tax	(8)	(11,129)	(99,312)
Other comprehensive income (loss), tax (expense) benefit
Other comprehensive income (loss), before reclassifications, tax (expense) benefit	122	(3,525)	(1,111)
Amounts reclassified from accumulated other comprehensive income (loss), tax (expense) benefit	2	4,057	36,173
Other comprehensive income (loss):
Other comprehensive income (loss), before reclassifications, net of tax	(407)	6,146	1,939
Amounts reclassified from accumulated other comprehensive income (loss), net of tax	$ (6)	$ (7,072)	$ (63,139)