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	(101,065)			(101,065)
Anti-dilution payments	3			3
Stock options exercised, shares		3,773
Stock-based compensation, net of tax	2,751	$ 3	4,033			$ (1,285)
Stock-based compensation, net of tax, shares		289,447				86,544
Net gain/ (loss) on investments	6				6
Net loss on derivative financial instruments	(5)				(5)
Ending Balance at Sep. 30, 2018	3,661,139	$ 1,444	2,015,430	1,848,623	(4)	$ (204,354)
Ending Balance, shares at Sep. 30, 2018		144,378,512				6,944,054
Beginning Balance at Jun. 30, 2018	3,710,730	$ 1,444	2,013,862	1,899,735	23	$ (204,334)
Beginning Balance, shares at Jun. 30, 2018		144,374,006				6,943,090
Net loss	(51,112)			(51,112)
Stock-based compensation, net of tax	1,548		1,568			$ (20)
Stock-based compensation, net of tax, shares		4,506				964
Net gain/ (loss) on investments	(25)				(25)
Net loss on derivative financial instruments	(2)				(2)
Ending Balance at Sep. 30, 2018	3,661,139	$ 1,444	2,015,430	1,848,623	(4)	$ (204,354)
Ending Balance, shares at Sep. 30, 2018		144,378,512				6,944,054
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	(282,444)			(282,444)
Stock-based compensation, net of tax	3,152	$ 4	4,529			$ (1,381)
Stock-based compensation, net of tax, shares		385,416				129,456
Net gain/ (loss) on investments	(32)				(32)
Net loss on derivative financial instruments	(5)				(5)
Ending Balance at Sep. 30, 2019	3,305,324	$ 1,448	2,022,672	1,486,971	(16)	$ (205,751)
Ending Balance, shares at Sep. 30, 2019		144,769,078				7,074,765
Beginning Balance at Jun. 30, 2019	3,398,897	$ 1,448	2,021,095	1,582,099	(6)	$ (205,739)
Beginning Balance, shares at Jun. 30, 2019		144,764,125				7,073,498
Net loss	(95,128)			(95,128)
Stock-based compensation, net of tax	1,565		1,577			$ (12)
Stock-based compensation, net of tax, shares		4,953				1,267
Net gain/ (loss) on investments	(8)				(8)
Net loss on derivative financial instruments	(2)				(2)
Ending Balance at Sep. 30, 2019	$ 3,305,324	$ 1,448	$ 2,022,672	$ 1,486,971	$ (16)	$ (205,751)
Ending Balance, shares at Sep. 30, 2019		144,769,078				7,074,765