CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Treasury Stock	Retained Earnings	Accumulated Other Comprehensive Loss
Beginning balance at Dec. 31, 2017	$ 1,257,455	$ 441,369	$ 1,808,391	$ (2,389,877)	$ 2,179,358	$ (781,786)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(311,253)				(311,253)
Other comprehensive income (loss), net of tax	42,637					42,637
Issuance of treasury stock for restricted stock units vesting	(1,648)		(5,675)	4,027
Share-based compensation	14,423		14,423
Ending balance at Mar. 31, 2018	982,466	441,369	1,817,139	(2,385,850)	1,848,957	(739,149)
Beginning balance at Dec. 31, 2017	1,257,455	441,369	1,808,391	(2,389,877)	2,179,358	(781,786)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(552,184)
Other comprehensive income (loss), net of tax	(42,292)
Ending balance at Jun. 30, 2018	663,971	441,369	1,820,432	(2,381,777)	1,608,025	(824,078)
Beginning balance at Mar. 31, 2018	982,466	441,369	1,817,139	(2,385,850)	1,848,957	(739,149)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(240,931)				(240,931)
Other comprehensive income (loss), net of tax	(84,929)					(84,929)
Issuance of treasury stock for restricted stock units vesting	(752)		(4,624)	3,872
Deferred compensation	124		(77)	201
Share-based compensation	7,994		7,994
Ending balance at Jun. 30, 2018	663,971	441,369	1,820,432	(2,381,777)	1,608,025	(824,078)
Beginning balance at Dec. 31, 2018	669,465	441,369	1,812,682	(2,354,617)	1,629,257	(859,226)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(183,718)				(183,718)
Other comprehensive income (loss), net of tax	21,292					21,292
Issuance of treasury stock for restricted stock units vesting	(387)		(1,829)	1,442
Share-based compensation	11,865		11,865
Ending balance at Mar. 31, 2019	518,517	441,369	1,822,718	(2,353,175)	1,445,539	(837,934)
Beginning balance at Dec. 31, 2018	669,465	441,369	1,812,682	(2,354,617)	1,629,257	(859,226)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(291,705)
Other comprehensive income (loss), net of tax	19,564
Ending balance at Jun. 30, 2019	421,337	441,369	1,831,952	(2,349,874)	1,337,552	(839,662)
Beginning balance at Mar. 31, 2019	518,517	441,369	1,822,718	(2,353,175)	1,445,539	(837,934)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(107,987)				(107,987)
Other comprehensive income (loss), net of tax	(1,728)					(1,728)
Issuance of treasury stock for restricted stock units vesting	(35)		(3,060)	3,025
Deferred compensation	125		(151)	276
Share-based compensation	12,445		12,445
Ending balance at Jun. 30, 2019	$ 421,337	$ 441,369	$ 1,831,952	$ (2,349,874)	$ 1,337,552	$ (839,662)