Consolidated Statement of Stockholders Equity (USD $) In Thousands, except Share data	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]
Beginning balance at Dec. 31, 2012	$ 894,928	$ 367	$ 561,963	$ 332,105	$ 493
Beginning balance, shares at Dec. 31, 2012	36,687,785	36,687,785
Net income	243,670			243,670
Other comprehensive loss, net of tax	(54)				(54)
Share-based compensation	9,801		9,801
Excess tax benefit on share-based compensation	896		896
Issuance of shares under incentive plans	2,127	3	2,124
Issuance of shares under incentive plans, shares		326,325
Ending balance at Sep. 30, 2013	$ 1,151,368	$ 370	$ 574,784	$ 575,775	$ 439
Ending balance, shares at Sep. 30, 2013	37,014,110	37,014,110