Condensed Consolidated Statements of Shareholders Equity - 6 months ended Jun. 30, 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	$ 476,410				476,410
Other comprehensive income, net of tax (unaudited)	18			18
Stock-based compensation (unaudited)	21,465		21,465
Restricted stock:
Granted (unaudited)	$ 13	$ 13
Granted (unaudited), shares	1,277,491	1,277,491
Repurchased and canceled (unaudited)	$ (15,619)	$ (3)	(15,616)
Repurchased and canceled (unaudited), shares	(287,506)	(287,506)
Forfeited (unaudited), shares	(178,957)	(178,957)
Forfeitures (unaudited)	$ (2)	$ (2)
Balance at Jun. 30, 2018	$ 5,613,488	$ 3,760	$ 1,415,175	$ 325	$ 4,194,228
Balance, shares at Jun. 30, 2018	376,030,797	376,030,797