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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net income	$ 139,371	$ 102,524	$ 1,616,900	$ 321,514
Weighted average common shares outstanding, basic	78,824	79,332	78,729	79,709
Dilutive effect of potential common stock	339	493	349	688
Total shares, diluted	79,163	79,825	79,078	80,397
Net income per share, basic	$ 1.77	$ 1.29	$ 20.54	$ 4.03
Net income per share, diluted	$ 1.76	$ 1.28	$ 20.45	$ 4.00
Anti-dilutive potential common shares	65	398	66	25
Retained Earnings
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net income	$ 139,371	$ 102,524	$ 1,616,900	$ 321,514