CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Common stock held in treasury	Additional paid-in capital	Retained (deficit)/earnings	Accumulated other comprehensive (loss) income
Beginning balance at Dec. 31, 2015	$ 2,759,658	$ 1,693	$ (2,245)	$ 2,442,623	$ 317,587	$ 0
Beginning balance Shares at Dec. 31, 2015		169,376,000
Issuance of common stock	3,048,653	$ 778	0	3,047,875	0	0
Issuance of common stock, shares		77,799,000
Stock-based compensation expense	37,023	$ 0	0	37,023	0	0
Tax benefit related to stock-based compensation	(2,062)	0	0	(2,062)	0	0
Cash dividends paid ($0.08 per share)	(16,682)	0	0	0	(16,682)	0
Cumulative-effect adjustment from adoption of ASU 2016-09	103,166	0	0	0	103,166	0
Treasury stock issuance		0	1,036	(1,036)	0	0
Net (loss) income	(521,388)	0	0	0	(521,388)	0
Ending balance at Dec. 31, 2016	5,408,368	$ 2,471	(1,209)	5,524,423	(117,317)	0
Ending balance Shares at Dec. 31, 2016		247,175,000
Issuance of common stock	2,987	$ 10	0	2,977	0	0
Issuance of common stock, shares		969,000
Stock-based compensation expense	50,942	$ 0	0	50,942	0	0
Cash dividends paid ($0.08 per share)	(19,839)	0	0	0	(19,839)	0
Treasury stock issuance		0	610	(610)	0	0
Other comprehensive income (loss)	(1,332)	0	0	0	0	(1,332)
Net (loss) income	333,146	0	0	0	333,146	0
Ending balance at Dec. 31, 2017	$ 5,774,272	$ 2,481	(599)	5,577,732	195,990	(1,332)
Ending balance Shares at Dec. 31, 2017	248,144,397	248,144,000
Issuance of common stock	$ 13,696	$ 14	0	13,682	0	0
Issuance of common stock, shares		1,374,000
Issuance of common stock upon vesting of PSUs		$ 0	0	31	(31)	0
Issuance of common stock upon vesting of PSUs, shares		2,000
Stock-based compensation expense	37,210	$ 0	0	37,210	0	0
Cash dividends paid ($0.08 per share)	(19,940)	0	0	0	(19,940)	0
Treasury stock issuance	0	0	208	(208)	0	0
Other comprehensive income (loss)	674	0	0	0	0	674
Net (loss) income	(1,746,481)	0	0	0	(1,746,481)	0
Ending balance at Dec. 31, 2018	$ 4,059,431	$ 2,495	$ (391)	$ 5,628,447	$ (1,570,462)	$ (658)
Ending balance Shares at Dec. 31, 2018	249,519,687	249,520,000