CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital		Retained Earnings		Accumulated Other Comprehensive Loss
Cash dividends per share	$ 0.10
Balances, Common Stock, Shares, Outstanding, Beginning at Dec. 31, 2014		67,463,060
Balances, Total stockholders' equity, beginning at Dec. 31, 2014	$ 2,286,655	$ 675	$ 283,295		$ 2,013,997		$ (11,312)
Increase (Decrease) in Stockholders' Equity
Net loss	(447,710)				(447,710)
Other comprehensive income (loss)	(2,090)						(2,090)
Cash dividends, $ 0.10 per share	(6,772)				(6,772)
Issuance of common stock under Employee Stock Purchase Plan (in shares)		197,214
Issuance of common stock under Employee Stock Purchase Plan	4,844	$ 2	4,842
Issuance of common stock upon vesting of RSUs and settlement of PSUs, net of shares used for tax withholdings (in shares)		375,523
Issuance of common stock upon vesting of RSUs and settlement of PSUs, net of shares used for tax withholdings	(8,678)	$ 4	(8,682)
Stock-based compensation expense (in shares)		39,903
Stock-based compensation expense	27,467	$ 0	27,467
Adjustments to Additional Paid in Capital, Other	(1,315)		(1,315)
Balances, Common Stock, Shares, Outstanding, Ending at Dec. 31, 2015		68,075,700
Balances, Total stockholders' equity, ending at Dec. 31, 2015	$ 1,852,401	$ 681	305,607		1,559,515		(13,402)
Cash dividends per share	$ 0.10
Increase (Decrease) in Stockholders' Equity
Net loss	$ (757,744)				(757,744)
Other comprehensive income (loss)	(1,154)						(1,154)
Cash dividends, $ 0.10 per share	(7,751)				(7,751)
Issuance of common stock under Employee Stock Purchase Plan (in shares)		218,135
Issuance of common stock under Employee Stock Purchase Plan	4,198	$ 2	4,196
Issuance of common stock upon vesting of RSUs and settlement of PSUs, net of shares used for tax withholdings (in shares)		199,243
Issuance of common stock upon vesting of RSUs and settlement of PSUs, net of shares used for tax withholdings	(2,354)	$ 2	(2,356)
Stock-based compensation expense (in shares)		53,473
Stock-based compensation expense	26,897	$ 1	26,896
Adjustments to Additional Paid in Capital, Other	(9,833)		(9,833)
Issuance of common stock from stock offerings, net of tax (in shares)		42,710,949
Issuance of common stock from stock offerings, net of tax	1,383,093	$ 427	1,382,666
Equity component of 1.50% Senior Convertible Notes due 2021 issuance, net of tax	33,575		33,575
Purchase of capped call transactions	$ (24,195)		(24,195)
Balances, Common Stock, Shares, Outstanding, Ending at Dec. 31, 2016	111,257,500	111,257,500
Balances, Total stockholders' equity, ending at Dec. 31, 2016	$ 2,497,133	$ 1,113	1,716,556		794,020		(14,556)
Increase (Decrease) in Stockholders' Equity
Cumulative effect of accounting change	$ 44,732		1,108	[1]	43,624	[1]
Cash dividends per share	$ 0.10
Net loss	$ (160,843)				(160,843)
Other comprehensive income (loss)	767						767
Cash dividends, $ 0.10 per share	(11,144)				(11,144)
Issuance of common stock under Employee Stock Purchase Plan (in shares)		186,665
Issuance of common stock under Employee Stock Purchase Plan	2,623	$ 2	2,621
Issuance of common stock upon vesting of RSUs and settlement of PSUs, net of shares used for tax withholdings (in shares)		171,278
Issuance of common stock upon vesting of RSUs and settlement of PSUs, net of shares used for tax withholdings	(1,240)	$ 1	(1,241)
Stock-based compensation expense (in shares)		71,573
Stock-based compensation expense	22,700	$ 1	22,699
Adjustments to Additional Paid in Capital, Other	$ (120)		(120)
Issuance of common stock from stock offerings, net of tax (in shares)	0
Balances, Common Stock, Shares, Outstanding, Ending at Dec. 31, 2017	111,687,016	111,687,016
Balances, Total stockholders' equity, ending at Dec. 31, 2017	$ 2,394,608	$ 1,117	$ 1,741,623		$ 665,657		$ (13,789)

[1] Refer to Recently Issued Accounting Standards in Note 1 – Summary of Significant Accounting Policies for additional information.