Earnings Per Share Level 4 (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net Income (Loss) Attributable to Parent [Abstract]
Net income attributable to common stockholders	$ 193,046		$ 68,935		$ 103,239		$ 81,988		$ 247,316		$ 56,164		$ 68,481		$ 174,702		$ 447,208	$ 546,663	$ 177,038
After tax interest on convertible debt																	0	52	43
Net income — diluted																	$ 447,208	$ 546,715	$ 177,081
Weighted average shares (denominator):
Weighted average shares — basic																	182,447	187,630	193,086
Convertible debt																	0	121	121
Weighted average shares — diluted																	186,972	192,246	196,042
Net income attributable to common stockholders, basic	$ 1.07	[1]	$ 0.38	[1]	$ 0.57	[1]	$ 0.44	[1]	$ 1.32	[1]	$ 0.30	[1]	$ 0.37	[1]	$ 0.93	[1]	$ 2.45	$ 2.91	$ 0.92
Net income attributable to common stockholders, diluted	$ 1.04	[1]	$ 0.37	[1]	$ 0.55	[1]	$ 0.43	[1]	$ 1.29	[1]	$ 0.29	[1]	$ 0.36	[1]	$ 0.91	[1]	$ 2.39	$ 2.84	$ 0.90
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount																	1,035,000	911,000	982,000
Stock Options [Member]
Weighted average shares (denominator):
Share based compensation																	4,339	4,396	2,823
Restricted Stock Units (RSUs) [Member]
Weighted average shares (denominator):
Share based compensation																	186	99	12

[1] Net income per share is computed independently for each of the quarters presented. Therefore, the sum of the quarters’ net income per share may not equal the total computed for the year.