Stockholders' Equity and Earnings Per Share (Details 3) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Basic
Net income	$ 118,330	$ 103,284	$ 288,066	$ 210,800
Basic weighted average number of shares outstanding (in shares)	144,485	144,101	144,368	144,029
Basic EPS (in dollars per share)	$ 0.82	$ 0.72	$ 2.00	$ 1.46
Diluted
Net income	$ 118,330	$ 103,284	$ 288,066	$ 210,800
Basic weighted average number of shares outstanding (in shares)	144,485	144,101	144,368	144,029
Diluted potential common shares (in shares)	1,255	977	1,406	944
Diluted weighted average number of shares outstanding (in shares)	145,740	145,078	145,774	144,973
Diluted EPS (in dollars per share)	$ 0.81	$ 0.71	$ 1.98	$ 1.45