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, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
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)	$ 187,843	$ 100,143	$ 75,496	$ 187,340	$ 121,425	$ 151,048	$ 194,302	$ 204,328	$ 550,822	$ 671,103	$ 1,258,379
Diluted earnings per share (in dollars)									$ 550,822	$ 671,103	$ 1,258,379
Weighted Average Shares (Denominator)
Basic earnings per share (in shares)									211,140,000	219,639,000	233,923,000
Dilutive common share equivalents (in shares)									1,205,000	1,109,000	1,270,000
Diluted earnings per share (in shares)									212,345,000	220,748,000	235,193,000
Per Share Amount
Basic (in dollars per share)	$ 0.89	$ 0.48	$ 0.36	$ 0.88	$ 0.56	$ 0.69	$ 0.88	$ 0.91	$ 2.61	$ 3.06	$ 5.38
Diluted (in dollars per share)	$ 0.89	$ 0.47	$ 0.36	$ 0.88	$ 0.56	$ 0.69	$ 0.87	$ 0.91	$ 2.59	$ 3.04	$ 5.35