Computation of Basic and Diluted Net Income Per Share Attributable to Common Stock (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net income	$ 102,524	$ 100,872	$ 321,514	$ 302,843
Weighted average common shares outstanding, basic	79,332	80,111	79,709	80,122
Dilutive effect of potential common stock	493	1,248	688	1,416
Total shares, diluted	79,825	81,359	80,397	81,538
Net income per share, basic	$ 1.29	$ 1.26	$ 4.03	$ 3.78
Net income per share, diluted	$ 1.28	$ 1.24	$ 4.00	$ 3.71
Retained Earnings
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net income	$ 102,524	$ 100,872	$ 321,514	$ 302,843