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		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net income	$ (40,602)	$ 147,142	$ 1,477,529	$ 218,990
Weighted average common shares outstanding, basic	78,769	79,943	78,681	79,901
Dilutive effect of potential common stock	0	647	335	764
Total shares, diluted	78,769	80,590	79,016	80,665
Net income (loss) per share, basic	$ (0.52)	$ 1.84	$ 18.78	$ 2.74
Net income (loss) per share, diluted	$ (0.52)	$ 1.83	$ 18.70	$ 2.71
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	733	139	231	111
Retained Earnings
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net income	$ (40,602)	$ 147,142	$ 1,477,529	$ 218,990