Earnings Per Share (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
Net Income (Loss) Attributable to Parent [Abstract]
Net income attributable to common stockholders	$ 72,329	$ 103,239	$ 151,652	$ 185,227
After tax interest on convertible debt	0	15	0	30
Net income — diluted	$ 72,329	$ 103,254	$ 151,652	$ 185,257
Weighted average shares (denominator):
Weighted average shares — basic	(182,369)	(182,637)	(182,048)	(183,877)
Convertible debt	0	121	0	121
Weighted average shares — diluted	185,690	187,188	185,517	188,547
Net income attributable to common stockholders, basic	$ 0.40	$ 0.57	$ 0.83	$ 1.01
Net income attributable to common stockholders, diluted	$ 0.39	$ 0.55	$ 0.82	$ 0.98
Equity Option [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Stock options	3,278	4,265	3,418	4,391
Restricted Stock Units (RSUs) [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Stock options	43	165	51	158
Equity Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	105	1,155	0	868