Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	1,523	1,799	1,212	2,362
Net Income (Loss) Attributable to Parent [Abstract]
Net income attributable to common stockholders	$ 68,481	$ 15,620	$ 243,183	$ 63,065
After tax interest on convertible debt	13	10	25	22
Net income — diluted	$ 68,494	$ 15,630	$ 243,208	$ 63,087
Weighted average shares (denominator):
Weighted average shares — basic	(187,597)	(193,806)	(187,927)	(194,366)
Convertible debt	121	121	121	121
Weighted average shares — diluted	192,138	196,718	192,511	197,463
Net income attributable to common stockholders, basic	$ 0.37	$ 0.08	$ 1.29	$ 0.32
Net income attributable to common stockholders, diluted	$ 0.36	$ 0.08	$ 1.26	$ 0.32
Equity Option [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Stock options	4,333	2,788	4,389	2,975
Restricted Stock Units (RSUs) [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Stock options	87	3	74	1
Equity Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	1,523	1,799	1,212	2,338
Restricted Stock Units (RSUs) [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	0	0	0	24