Summary of Significant Accounting and Reporting Policies (Schedule of Earnings Per Share, Basic And Diluted) (Details) - USD ($)	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
Basic Earnings Per Share
Net income	$ 99,547,000	$ 111,898,000	$ 108,959,000	$ 104,280,000	$ 106,275,000	$ 111,336,000	$ 109,024,000	$ 111,249,000	$ 424,683,939	$ 437,883,097	$ 406,791,922
Less: Allocated to participating securities									5,028,813	3,836,536	2,562,473
Net Income available to common shareholders									$ 419,655,126	$ 437,883,097	$ 406,791,922
Basic weighted average shares outstanding (in shares)									251,766,382	267,794,786	285,864,997
Net Income per share - Basic (in dollars per share)	$ 0.39	$ 0.44	$ 0.42	$ 0.40	$ 0.41	$ 0.42	$ 0.40	$ 0.40	$ 1.67	$ 1.64	$ 1.42
Diluted Earnings Per Share
Allocation of Net Income used in basic computation									$ 419,655,126	$ 437,883,097	$ 406,791,922
Reallocation of undistributed earnings									21,104	21,007	19,398
Net Income available to common shareholders - Diluted									$ 419,676,230	$ 437,904,104	$ 406,811,320
Basic weighted average shares outstanding (in shares)									251,766,382	267,794,786	285,864,997
Additional weighted average dilutive common stock equivalents (in shares)									1,506,608	2,082,563	2,361,092
Diluted weighted average shares outstanding (in shares)									253,272,990	269,877,349	288,226,089
Net income per share - Diluted (in dollars per share)	$ 0.39	$ 0.44	$ 0.42	$ 0.40	$ 0.41	$ 0.42	$ 0.40	$ 0.40	$ 1.66	$ 1.62	$ 1.41