Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Gains (Losses) [Member]	Treasury Stock [Member]
Beginning Balance at Dec. 31, 2017	$ 3,774,261	$ 1,441	$ 2,011,397	$ 1,964,497	$ (5)	$ (203,069)
Beginning Balance, shares at Dec. 31, 2017		144,085,292				6,857,510
Impact of change in accounting principle at Dec. 31, 2017	(14,812)			(14,812)
Adjusted balance at Dec. 31, 2017	3,759,449	$ 1,441	2,011,397	1,949,685	(5)	$ (203,069)
Adjusted balance, shares at Dec. 31, 2017		144,085,292				6,857,510
Net loss	(49,953)			(49,953)
Anti-dilution adjustment/ payments	3			3
Stock options exercised, shares		3,773
Stock-based compensation, net of tax	1,203	$ 3	2,465			$ (1,265)
Stock-based compensation, net of tax, shares		284,941				85,580
Net gain/ (loss) on investments	31				31
Net loss on derivative financial instruments	(3)				(3)
Ending Balance at Jun. 30, 2018	3,710,730	$ 1,444	2,013,862	1,899,735	23	$ (204,334)
Ending Balance, shares at Jun. 30, 2018		144,374,006				6,943,090
Beginning Balance at Mar. 31, 2018	3,779,632	$ 1,442	2,012,993	1,969,006	(7)	$ (203,802)
Beginning Balance, shares at Mar. 31, 2018		144,249,563				6,906,592
Net loss	(69,274)			(69,274)
Anti-dilution adjustment/ payments	3			3
Stock options exercised, shares		3,773
Stock-based compensation, net of tax	339	$ 2	869			$ (532)
Stock-based compensation, net of tax, shares		120,670				36,498
Net gain/ (loss) on investments	31				31
Net loss on derivative financial instruments	(1)				(1)
Ending Balance at Jun. 30, 2018	3,710,730	$ 1,444	2,013,862	1,899,735	23	$ (204,334)
Ending Balance, shares at Jun. 30, 2018		144,374,006				6,943,090
Beginning Balance at Dec. 31, 2018	3,584,653	$ 1,444	2,018,143	1,769,415	21	$ (204,370)
Beginning Balance, shares at Dec. 31, 2018		144,383,662				6,945,309
Net loss	(187,316)			(187,316)
Stock-based compensation, net of tax	1,587	$ 4	2,952			$ (1,369)
Stock-based compensation, net of tax, shares		380,463				128,189
Net gain/ (loss) on investments	(24)				(24)
Net loss on derivative financial instruments	(3)				(3)
Ending Balance at Jun. 30, 2019	3,398,897	$ 1,448	2,021,095	1,582,099	(6)	$ (205,739)
Ending Balance, shares at Jun. 30, 2019		144,764,125				7,073,498
Beginning Balance at Mar. 31, 2019	3,511,876	$ 1,446	2,019,555	1,696,087	2	$ (205,214)
Beginning Balance, shares at Mar. 31, 2019		144,606,992				7,026,789
Net loss	(113,988)			(113,988)
Stock-based compensation, net of tax	1,017	$ 2	1,540			$ (525)
Stock-based compensation, net of tax, shares		157,133				46,709
Net gain/ (loss) on investments	(6)				(6)
Net loss on derivative financial instruments	(2)				(2)
Ending Balance at Jun. 30, 2019	$ 3,398,897	$ 1,448	$ 2,021,095	$ 1,582,099	$ (6)	$ (205,739)
Ending Balance, shares at Jun. 30, 2019		144,764,125				7,073,498