Consolidated Statement of Changes in Stockholders' Equity (USD $) In Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings (Accumulated Deficit)
Beginning Balance at Dec. 31, 2012	$ 78,924	$ 6	$ 84,308	$ (5,390)
Beginning Balance (in shares) at Dec. 31, 2012		64,628
Net income	25,857			25,857
Restricted stock vestings (in shares)		397
Restricted stock vestings	83		83
Dividend equivalents cancelled upon forfeiture of performance-based restricted stock awards	50		50
Shares surrendered and cancelled upon vesting of restricted stock to satisfy tax withholdings (in shares)		(124)
Shares surrendered and cancelled upon vesting of restricted stock to satisfy tax withholdings	(2,242)		(2,242)
Stock-based compensation	3,267		3,267
Tax deductions relating to stock-based compensation	1,335		1,335
Shares issuable in lieu of dividend payments on unvested performance-based restricted stock awards	(133)		(133)
Issuance of common stock under employee stock purchase plan (in shares)		88
Issuance of common stock under employee stock purchase plan	904		904
Ending Balance at Sep. 30, 2013	$ 108,045	$ 6	$ 87,572	$ 20,467
Ending Balance (in shares) at Sep. 30, 2013		64,989