CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Common stock held in treasury	Additional paid-in capital	Retained earnings/(deficit)	Accumulated other comprehensive (loss)
Beginning balance at Dec. 31, 2014	$ 3,457,429	$ 1,687	$ (3,088)	$ 2,400,475	$ 1,058,355	$ 0
Beginning balance Shares at Dec. 31, 2014		168,711,000
Issuance of common stock	10,073	$ 6	0	10,067	0	0
Issuance of common stock, shares		665,000
Stock-based compensation expense	36,496	$ 0	0	36,496	0	0
Tax benefit related to stock-based compensation	(3,572)	0	0	(3,572)	0	0
Common dividends declared ($0.16 per share for 2015 and $0.08 per share for 2016, 2017)	(27,083)	0	0	0	(27,083)	0
Treasury stock issuance		0	843	(843)	0	0
Net income (loss)	(713,685)	0	0	0	(713,685)	0
Ending balance at Dec. 31, 2015	2,759,658	$ 1,693	(2,245)	2,442,623	317,587	0
Ending 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
Common dividends declared ($0.16 per share for 2015 and $0.08 per share for 2016, 2017)	(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 income (loss)	(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	247,174,903	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
Common dividends declared ($0.16 per share for 2015 and $0.08 per share for 2016, 2017)	(19,839)	0	0	0	(19,839)	0
Treasury stock issuance	0	0	610	(610)	0	0
Other comprehensive loss	(1,332)	0	0	0	0	(1,332)
Net income (loss)	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