Description of the Business and Summary of Significant Accounting Policies (Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share
Antidilutive common share equivalents excluded from computation of earnings per share amount (in shares)									0	0	0
Net Income (Numerator)
Basic earnings per share (in dollars)	$ 121,425	$ 151,048	$ 194,302	$ 204,328	$ 270,004	$ 398,375	$ 362,449	$ 227,551	$ 671,103	$ 1,258,379	$ 812,741
Dilutive earnings per share (in dollars)
Diluted earnings per share (in dollars)									$ 671,103	$ 1,258,379	$ 812,741
Weighted Average Shares (Denominator)
Basic earnings per share (in shares)									219,639,000	233,923,000	240,132,000
Dilutive common share equivalents (in shares)									1,109,000	1,270,000	1,649,000
Diluted earnings per share (in shares)									220,748,000	235,193,000	241,781,000
Per Share Amount
Basic (in dollars per share)	$ 0.56	$ 0.69	$ 0.88	$ 0.91	$ 1.18	$ 1.70	$ 1.54	$ 0.96	$ 3.06	$ 5.38	$ 3.38
Diluted (in dollars per share)	$ 0.56	$ 0.69	$ 0.87	$ 0.91	$ 1.17	$ 1.69	$ 1.53	$ 0.96	$ 3.04	$ 5.35	$ 3.36