Consolidated Statements of Comprehensive (Loss) Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net loss	$ (20,311)	$ (30,117)
Other comprehensive income (loss)
Amortization of accumulated actuarial gains and prior service costs, pension	120	594
Adjustments to accumulated actuarial gains and transition obligations, pension	(193)	136
Amortization of accumulated actuarial gains, transition obligations, and prior service costs, postretirement medical benefits	969	964
Tax effect of other comprehensive income	(45)	(958)
Foreign currency translation adjustment (losses) gains	(7,289)	2,103
Unrealized and realized (losses) gains on available-for-sale debt securities	(31)	810
Other comprehensive (loss) income, net of income taxes	(6,469)	3,649
Comprehensive loss	(26,780)	(26,468)
Less: Comprehensive loss attributable to noncontrolling interest	(722)	(499)
Comprehensive loss attributable to common shareholders	$ (26,058)	$ (25,969)