Net Income Per Share - Schedule of Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income - basic and diluted	$ 594,655	$ 388,317	$ 1,624,047	$ 1,024,992
Weighted average shares outstanding - basic (in shares)	108,033	106,706	107,828	106,108
Effect of dilutive securities:
Dilutive potential shares (in shares)	7,055	10,322	7,015	9,886
Weighted average shares - diluted (in shares)	115,088	117,028	114,843	115,994
Net income per share - basic (in dollars per share)	$ 5.50	$ 3.64	$ 15.06	$ 9.66
Net income per share - diluted (in dollars per share)	$ 5.17	$ 3.32	$ 14.14	$ 8.84
Stock options
Effect of dilutive securities:
Effect of dilutive securities (in shares)	7,027	9,809	6,999	9,386
Restricted stock
Effect of dilutive securities:
Effect of dilutive securities (in shares)	28	513	16	500