Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Statement of Comprehensive Income [Abstract]
Net (loss) income	$ (37,300)	$ 26,909
Other comprehensive income (loss)
Amortization of accumulated actuarial gains, pension	594	573
Adjustments to accumulated actuarial gains and transition obligations, pension	136	172
Amortization of accumulated actuarial gains, transition obligations, and prior service costs, postretirement medical benefit	964	200
Adjustments to accumulated actuarial losses and transition obligations, postretirement medical benefit	0	(688)
Tax effect of other comprehensive income losses	(572)	(57)
Change in foreign currency translation adjustment	2,103	19,175
Unrealized and realized gains and losses on available-for-sale securities	810	(281)
Other comprehensive income, net of income taxes	4,035	19,094
Comprehensive (loss) income	(33,265)	46,003
Less: Comprehensive loss attributable to noncontrolling interest	(499)	(498)
Comprehensive (loss) income attributable to common shareholders	$ (32,766)	$ 46,501