Condensed Consolidated Statements of Shareholders Equity - 3 months ended Mar. 31, 2018 - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Retained Earnings [Member]
Balance at Dec. 31, 2017	$ 5,131,203	$ 3,752	$ 1,409,326	$ 307	$ 3,717,818
Balance, shares at Dec. 31, 2017	375,219,769	375,219,769
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 233,946				233,946
Other comprehensive income, net of tax (unaudited)	2			2
Stock-based compensation (unaudited)	10,905		10,905
Restricted stock:
Granted (unaudited)	$ 12	$ 12
Granted (unaudited), shares	1,180,032	1,180,032
Repurchased and canceled (unaudited)	$ (14,846)	$ (3)	(14,843)
Repurchased and canceled (unaudited), shares	(276,108)	(276,108)
Forfeited (unaudited), shares	(66,489)	(66,489)
Forfeitures (unaudited)	$ (1)	$ (1)
Balance at Mar. 31, 2018	$ 5,361,221	$ 3,760	$ 1,405,388	$ 309	$ 3,951,764
Balance, shares at Mar. 31, 2018	376,057,204	376,057,204