Other Comprehensive Income (Loss) - Other comprehensive income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Other comprehensive income (loss), before tax amount
Other comprehensive income (loss), before tax amount	$ 810	$ (26,456)	$ 7,177	$ (93,747)
Other comprehensive income (loss), tax (expense) benefit
Other comprehensive income (loss), tax (expense) benefit	(62)	9,239	(2,326)	34,156
Other comprehensive income (loss):
Other comprehensive income (loss), net of tax	748	(17,217)	4,851	(59,591)
Foreign Currency Translation Adjustment
Other comprehensive income (loss), before tax amount
Other comprehensive income (loss), before reclassifications, before tax	639		846
Other comprehensive income (loss):
Other comprehensive income (loss), before reclassifications, net of tax	639		846
Unrealized/Recognized Gains (Losses)
Other comprehensive income (loss), before tax amount
Other comprehensive income (loss), before reclassifications, before tax	801	2,497	6,965	(104)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	(630)	(28,953)	(634)	(93,643)
Other comprehensive income (loss), tax (expense) benefit
Other comprehensive income (loss), before reclassifications, tax (expense) benefit	(290)	(916)	(2,559)	38
Amounts reclassified from accumulated other comprehensive income (loss), tax (expense) benefit	228	10,155	233	34,118
Other comprehensive income (loss):
Other comprehensive income (loss), before reclassifications, net of tax	511	1,581	4,406	(66)
Amounts reclassified from accumulated other comprehensive income (loss), net of tax	$ (402)	$ (18,798)	$ (401)	$ (59,525)