Stockholders' Equity and Earnings Per Share (Details 3) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Basic
Net income	$ 132,660	$ 110,143	$ 420,726	$ 320,943
Basic weighted average number of shares outstanding (in shares)	144,498	144,122	144,412	144,061
Basic EPS (in dollars per share)	$ 0.92	$ 0.76	$ 2.91	$ 2.23
Diluted
Net income	$ 132,660	$ 110,143	$ 420,726	$ 320,943
Basic weighted average number of shares outstanding (in shares)	144,498	144,122	144,412	144,061
Diluted potential common shares (in shares)	1,384	1,116	1,437	1,025
Diluted weighted average number of shares outstanding (in shares)	145,882	145,238	145,849	145,086
Diluted EPS (in dollars per share)	$ 0.91	$ 0.76	$ 2.88	$ 2.21