Consolidated statement of stockholders' equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional paid-in capital	Treasury Stock (at cost)	Accumulated deficit
Increase (Decrease) in Stockholders' Equity
Adjustment to the beginning balance of accumulated deficit upon adoption of ASC 606 (see Note 4.a) | Accounting Standards Update 2014-09	$ 141,118				$ 141,118
Balance, beginning of period (in shares) at Dec. 31, 2017		242,521		0
Balance, beginning of period at Dec. 31, 2017	765,579	$ 2,425	$ 2,432,262	$ 0	(1,669,108)
Increase (Decrease) in Stockholders' Equity
Restricted stock awards (in shares)		3,052
Restricted stock awards	0	$ 30	(30)
Restricted stock forfeitures (in shares)		(13)
Restricted stock forfeitures	0	$ 0	0
Share repurchases (in shares)				6,728
Share repurchases	(58,475)			$ (58,475)
Vested stock exchanged for tax withholding (in shares)				512
Vested stock exchanged for tax withholding	(4,353)			$ (4,353)
Retirement of treasury stock (in shares)		(7,240)		(7,240)
Retirement of treasury stock	0	$ (72)	(62,756)	$ 62,828
Stock-based compensation	11,441		11,441
Net income	86,520				86,520
Balance, end of period (in shares) at Mar. 31, 2018		238,320		0
Balance, end of period at Mar. 31, 2018	$ 941,830	$ 2,383	$ 2,380,917	$ 0	$ (1,441,470)