Condensed Consolidated Statements of Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Retained (Loss) Earnings	Treasury Stock
Beginning Balances at Dec. 31, 2017	$ (1,154,636)	$ 2,116,018	$ (3,270,605)	$ (49)
Beginning Balances, Shares at Dec. 31, 2017		196,347
Employee stock plan grants, Shares		1,226
Net share settlements	(2,061)		(2,061)
Net share settlements, Shares		(519)
Fair value of employee stock plan grants	10,709	$ 10,709
Net income (loss)	47,488		47,488
Initial adoption | ASC 606	1,761		1,761
Ending Balances at Mar. 31, 2018	(1,096,739)	$ 2,126,727	(3,223,417)	(49)
Ending Balances, Shares at Mar. 31, 2018		197,054
Beginning Balances at Dec. 31, 2017	(1,154,636)	$ 2,116,018	(3,270,605)	(49)
Beginning Balances, Shares at Dec. 31, 2017		196,347
Net income (loss)	26,933
Ending Balances at Jun. 30, 2018	(1,114,830)	$ 2,129,191	(3,243,972)	(49)
Ending Balances, Shares at Jun. 30, 2018		197,054
Beginning Balances at Mar. 31, 2018	(1,096,739)	$ 2,126,727	(3,223,417)	(49)
Beginning Balances, Shares at Mar. 31, 2018		197,054
Fair value of employee stock plan grants	2,464	$ 2,464
Net income (loss)	(20,555)		(20,555)
Ending Balances at Jun. 30, 2018	(1,114,830)	$ 2,129,191	(3,243,972)	(49)
Ending Balances, Shares at Jun. 30, 2018		197,054
Beginning Balances at Dec. 31, 2018	(1,048,622)	$ 2,137,443	(3,186,016)	(49)
Beginning Balances, Shares at Dec. 31, 2018		197,383
Fair value of employee stock plan grants	1,127	$ 1,127
Net income (loss)	40,674		40,674
Initial adoption | ASC 842	92,818		92,818
Ending Balances at Mar. 31, 2019	(914,003)	$ 2,138,570	(3,052,524)	(49)
Ending Balances, Shares at Mar. 31, 2019		197,383
Beginning Balances at Dec. 31, 2018	(1,048,622)	$ 2,137,443	(3,186,016)	(49)
Beginning Balances, Shares at Dec. 31, 2018		197,383
Net income (loss)	97,780
Ending Balances at Jun. 30, 2019	(856,225)	$ 2,139,314	(2,995,490)	(49)
Ending Balances, Shares at Jun. 30, 2019		197,840
Beginning Balances at Mar. 31, 2019	(914,003)	$ 2,138,570	(3,052,524)	(49)
Beginning Balances, Shares at Mar. 31, 2019		197,383
Stock plan grants, Shares		648
Net share settlements	(71)		(71)
Net share settlements, Shares		(191)
Fair value of employee stock plan grants	744	$ 744
Net income (loss)	57,105		57,105
Ending Balances at Jun. 30, 2019	$ (856,225)	$ 2,139,314	$ (2,995,490)	$ (49)
Ending Balances, Shares at Jun. 30, 2019		197,840