Condensed Consolidated Statements of Shareholders Equity - 9 months ended Sep. 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	$ 790,580
Other comprehensive income, net of tax (unaudited)	123			123
Stock-based compensation (unaudited)	33,196		33,196
Restricted stock:
Granted (unaudited)	$ 13	$ 13
Granted (unaudited), shares	1,332,705	1,332,705
Repurchased and canceled (unaudited)	$ (16,303)	$ (3)	(16,300)
Repurchased and canceled (unaudited), shares	(298,648)	(298,648)
Forfeited (unaudited), shares	(258,532)	(258,532)
Forfeitures (unaudited)	$ (2)	$ (2)
Balance at Sep. 30, 2018	$ 5,938,810	$ 3,760	$ 1,426,222	$ 430	$ 4,508,398
Balance, shares at Sep. 30, 2018	375,995,294	375,995,294