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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Net income	$ 147,142	$ 106,105	$ 218,990	$ 201,971
Weighted average common shares outstanding, basic	79,943	80,216	79,901	80,127
Dilutive effect of potential common stock	647	1,255	764	1,448
Total shares, diluted	80,590	81,471	80,665	81,575
Net income per share, basic	$ 1.84	$ 1.32	$ 2.74	$ 2.52
Net income per share, diluted	$ 1.83	$ 1.30	$ 2.71	$ 2.48