Consolidated Statements of Shareholders' Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common stock	Additional paid-in capital	Retained earnings
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	0	13
Exercised, shares		18,470
Repurchased and canceled	(150)	0	(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, shares		(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
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
Stock options:
Exercised	60		60
Exercised, shares	18,470	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, shares		(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
Net income	764,219			764,219
Stock-based compensation	39,888		39,888
Stock options:
Exercised, shares	86,500
Restricted stock:
Issued	3	3
Issued, shares		261,259
Repurchased and canceled	(14,690)	(1)	(14,689)
Repurchased and canceled, shares		(138,525)
Forfeited	(1)	(1)
Forfeited, shares		(68,756)
Balance at Dec. 31, 2013	$ 3,953,118	$ 1,857	$ 1,252,034	$ 2,699,227
Balance, shares at Dec. 31, 2013	185,658,659	185,658,659