Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net loss	$ (191,327)	$ (46,282)	$ (211,638)	$ (76,398)
Other comprehensive income (loss)
Amortization of accumulated actuarial gains and prior service costs, pension	119	583	239	1,177
Adjustments to accumulated actuarial gains and transition obligations, pension	148	165	(45)	301
Amortization of accumulated actuarial gains, transition obligations, and prior service costs, postretirement medical benefits	969	965	1,938	1,929
Tax effect of other comprehensive income	(857)	(1,247)	(902)	(2,205)
Foreign currency translation adjustment (losses) gains	(5,255)	5,926	(12,544)	8,029
Unrealized and realized (losses) gains on available-for-sale debt securities	(246)	386	(276)	1,196
Other comprehensive (loss) income, net of income taxes	(5,122)	6,778	(11,590)	10,427
Comprehensive loss	(196,449)	(39,504)	(223,228)	(65,971)
Less: Comprehensive loss attributable to noncontrolling interest	(5,260)	(138)	(5,982)	(637)
Comprehensive loss attributable to common shareholders	$ (191,189)	$ (39,366)	$ (217,246)	$ (65,334)