CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (UNAUDITED) (in thousands, except share data and dividends per share) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss
Cash dividends per share	$ 0.05
Balances, Common Stock, Shares, Outstanding, Beginning at Dec. 31, 2017		111,687,016
Balances, Total Stockholders' Equity, Beginning at Dec. 31, 2017	$ 2,394,608	$ 1,117	$ 1,741,623	$ 665,657	$ (13,789)
Increase (Decrease) in Stockholders' Equity
Net income (loss)	317,401			317,401
Other comprehensive income	260				260
Cash dividends declared, $0.05 per share	(5,584)			(5,584)
Stock-based compensation expense (Amount)	5,412		5,412
Other (AOCI)	0			1	(1)
Balances, Common Stock, Shares, Outstanding, Ending at Mar. 31, 2018		111,687,016
Balances, Total Stockholders' Equity, Ending at Mar. 31, 2018	$ 2,712,097	$ 1,117	1,747,035	980,444	(16,499)
Cash dividends per share	$ 0.05
Balances, Common Stock, Shares, Outstanding, Beginning at Dec. 31, 2017		111,687,016
Balances, Total Stockholders' Equity, Beginning at Dec. 31, 2017	$ 2,394,608	$ 1,117	1,741,623	665,657	(13,789)
Increase (Decrease) in Stockholders' Equity
Net income (loss)	334,598
Other comprehensive income	458
Balances, Common Stock, Shares, Outstanding, Ending at Jun. 30, 2018		111,846,998
Balances, Total Stockholders' Equity, Ending at Jun. 30, 2018	2,736,627	$ 1,118	1,754,169	997,641	(16,301)
Increase (Decrease) in Stockholders' Equity
Cumulative effect of accounting change	$ 0			2,969	(2,969)
Cash dividends per share	$ 0
Balances, Common Stock, Shares, Outstanding, Beginning at Mar. 31, 2018		111,687,016
Balances, Total Stockholders' Equity, Beginning at Mar. 31, 2018	$ 2,712,097	$ 1,117	1,747,035	980,444	(16,499)
Increase (Decrease) in Stockholders' Equity
Net income (loss)	17,197			17,197
Other comprehensive income	198				198
Issuance of common stock under Employee Stock Purchase Plan (Shares)		100,249
Issuance of common stock under Employee Stock Purchase Plan (Amount)	1,881	$ 1	1,880
Issuance of common stock upon vesting of RSUs, net of shares used for tax withholdings (Shares)		1,161
Issuance of common stock upon vesting of RSUs, net of shares used for tax withholdings (Amount)	(10)	$ 0	(10)
Stock-based compensation expense (Shares)		58,572
Stock-based compensation expense (Amount)	5,264	$ 0	5,264
Balances, Common Stock, Shares, Outstanding, Ending at Jun. 30, 2018		111,846,998
Balances, Total Stockholders' Equity, Ending at Jun. 30, 2018	$ 2,736,627	$ 1,118	1,754,169	997,641	(16,301)
Cash dividends per share	$ 0.05
Balances, Common Stock, Shares, Outstanding, Beginning at Dec. 31, 2018	112,241,966	112,241,966
Balances, Total Stockholders' Equity, Beginning at Dec. 31, 2018	$ 2,920,322	$ 1,122	1,765,738	1,165,842	(12,380)
Increase (Decrease) in Stockholders' Equity
Net income (loss)	(177,568)			(177,568)
Other comprehensive income	263				263
Cash dividends declared, $0.05 per share	(5,612)			(5,612)
Issuance of common stock upon vesting of RSUs, net of shares used for tax withholdings (Shares)		2,579
Issuance of common stock upon vesting of RSUs, net of shares used for tax withholdings (Amount)	(18)	$ 0	(18)
Stock-based compensation expense (Amount)	5,838		5,838
Balances, Common Stock, Shares, Outstanding, Ending at Mar. 31, 2019		112,244,545
Balances, Total Stockholders' Equity, Ending at Mar. 31, 2019	$ 2,743,225	$ 1,122	1,771,558	982,662	(12,117)
Cash dividends per share	$ 0.05
Balances, Common Stock, Shares, Outstanding, Beginning at Dec. 31, 2018	112,241,966	112,241,966
Balances, Total Stockholders' Equity, Beginning at Dec. 31, 2018	$ 2,920,322	$ 1,122	1,765,738	1,165,842	(12,380)
Increase (Decrease) in Stockholders' Equity
Net income (loss)	(127,180)
Other comprehensive income	$ 382
Balances, Common Stock, Shares, Outstanding, Ending at Jun. 30, 2019	112,525,633	112,525,633
Balances, Total Stockholders' Equity, Ending at Jun. 30, 2019	$ 2,801,843	$ 1,125	1,779,665	1,033,051	(11,998)
Cash dividends per share	$ 0
Balances, Common Stock, Shares, Outstanding, Beginning at Mar. 31, 2019		112,244,545
Balances, Total Stockholders' Equity, Beginning at Mar. 31, 2019	$ 2,743,225	$ 1,122	1,771,558	982,662	(12,117)
Increase (Decrease) in Stockholders' Equity
Net income (loss)	50,388			50,388
Other comprehensive income	119				119
Issuance of common stock under Employee Stock Purchase Plan (Shares)		184,079
Issuance of common stock under Employee Stock Purchase Plan (Amount)	1,959	$ 2	1,957
Issuance of common stock upon vesting of RSUs, net of shares used for tax withholdings (Shares)		290
Issuance of common stock upon vesting of RSUs, net of shares used for tax withholdings (Amount)	(2)	$ 0	(2)
Stock-based compensation expense (Shares)		96,719
Stock-based compensation expense (Amount)	6,154	$ 1	6,153
Other (APIC)	$ 0		(1)	1
Balances, Common Stock, Shares, Outstanding, Ending at Jun. 30, 2019	112,525,633	112,525,633
Balances, Total Stockholders' Equity, Ending at Jun. 30, 2019	$ 2,801,843	$ 1,125	$ 1,779,665	$ 1,033,051	$ (11,998)