Consolidated Statements of Shareholders' Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]
Balance at Dec. 31, 2009	$ 1,030,279	$ 1,700	$ 430,283	$ 598,296
Balance, shares at Dec. 31, 2009		169,968,471
Net income	168,255			168,255
Stock-based compensation	11,691		11,691
Excess tax benefit on stock-based compensation	5,230		5,230
Stock options:
Exercised	257	2	255
Exercised, shares	207,220	207,220
Repurchased and canceled	(2,662)	(1)	(2,661)
Repurchased and canceled, shares		(59,877)
Restricted stock:
Issued	4	4
Issued, shares		449,114
Repurchased and canceled	(4,899)	(1)	(4,898)
Repurchased and canceled, shares		(100,561)
Forfeited		(55,715)
Balance at Dec. 31, 2010	1,208,155	1,704	439,900	766,551
Balance, shares at Dec. 31, 2010		170,408,652
Net income	429,072			429,072
Public offering of common stock	659,232	101	659,131
Public offering of common stock, shares		10,080,000
Stock-based compensation	16,567		16,567
Stock options:
Exercised	13		13
Exercised, shares	18,470	18,470
Repurchased and canceled	(150)		(150)
Repurchased and canceled, shares		(2,495)
Restricted stock:
Issued	5	5
Issued, shares		491,315
Repurchased and canceled	(4,768)	(1)	(4,767)
Repurchased and canceled, shares		(82,807)
Forfeited		(41,447)
Balance at Dec. 31, 2011	2,308,126	1,809	1,110,694	1,195,623
Balance, shares at Dec. 31, 2011	180,871,688	180,871,688
Net income	739,385			739,385
Common stock issued in exchange for assets	81,528	39	81,489
Common stock issued in exchange for assets, shares		3,916,157
Stock-based compensation	30,209		30,209
Excess tax benefit on stock-based compensation	15,618		15,618
Stock options:
Exercised	60		60
Exercised, shares	86,500	86,500
Repurchased and canceled	(2,951)		(2,951)
Repurchased and canceled, shares		(32,984)
Restricted stock:
Issued	9	9
Issued, shares		916,028
Repurchased and canceled	(8,285)	(1)	(8,284)
Repurchased and canceled, shares		(112,521)
Forfeited		(40,187)
Balance at Dec. 31, 2012	$ 3,163,699	$ 1,856	$ 1,226,835	$ 1,935,008
Balance, shares at Dec. 31, 2012	185,604,681	185,604,681