CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Balance at Dec. 31, 2012	$ 738,801	$ 344	$ 139,046	$ 600,811	$ (1,400)
Balance (in shares) at Dec. 31, 2012		34,400
Increase (Decrease) in Stockholders' Equity
Stock compensation expense			13,136
Compensation expenses recorded	13,136
Stock compensation expense (in shares)		15
Exercise of stock options	52		52
Exercise of stock options (in shares)		8
Shares issued upon vesting		$ 2	(2)
Shares issued upon vesting (in shares)		195
Excess tax benefit from stock compensation	319		319
Shares withheld for taxes	(8,635)		(8,635)
Net income (loss)	145,689			145,689
Total other comprehensive income (loss)	(1,243)				(1,243)
Balance at Dec. 31, 2013	888,119	$ 346	143,916	746,500	(2,643)
Balance (in shares) at Dec. 31, 2013		34,618
Increase (Decrease) in Stockholders' Equity
Stock compensation expense			2,865
Compensation expenses recorded	2,865
Stock compensation expense (in shares)		5
Shares issued upon vesting (in shares)		1
Shares withheld for taxes	(50)		(50)
Net income (loss)	(2,685)			(2,685)
Total other comprehensive income (loss)	600				600
Balance at Mar. 31, 2014	888,849	$ 346	146,731	743,815	(2,043)
Balance (in shares) at Mar. 31, 2014		34,624
Increase (Decrease) in Stockholders' Equity
Stock compensation expense			13,524	0	0
Compensation expenses recorded	13,524
Stock compensation expense (in shares)		11
Shares issued upon vesting		$ 1	(1)
Shares issued upon vesting (in shares)		93
Excess tax benefit from stock compensation	4,197		4,197
Shares withheld for taxes	(5,674)		(5,674)
Stock repurchase	(107,239)	$ (14)		(107,225)
Stock repurchase (in shares)		(1,436)
Net income (loss)	161,780			161,780
Total other comprehensive income (loss)	(18,425)				(18,425)
Balance at Mar. 31, 2015	937,012	$ 333	158,777	798,370	(20,468)
Balance (in shares) at Mar. 31, 2015		33,292
Increase (Decrease) in Stockholders' Equity
Stock compensation expense	6,622		6,622	0	0
Compensation expenses recorded	6,622
Stock compensation expense (in shares)		16
Shares issued upon vesting		$ 1	(1)
Shares issued upon vesting (in shares)		132
Excess tax benefit from stock compensation	471		471
Shares withheld for taxes	(4,610)		(4,610)
Stock repurchase	(94,200)	$ (14)		(94,186)
Stock repurchase (in shares)		(1,420)
Net income (loss)	122,265			122,265
Total other comprehensive income (loss)	(89)				(89)
Balance at Mar. 31, 2016	$ 967,471	$ 320	$ 161,259	$ 826,449	$ (20,557)
Balance (in shares) at Mar. 31, 2016		32,020