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, 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
Basic Earnings Per Share
Net income	$ 143,339,000	$ 117,093,000	$ (2,374,000)	$ 89,506,000	$ 99,547,000	$ 111,898,000	$ 108,959,000	$ 104,280,000	$ 347,563,621		$ 424,683,939		$ 437,883,097
Less: Allocated to participating securities									4,964,928		5,028,813		3,836,536
Net Income available to common shareholders									$ 342,598,693		$ 419,655,126		$ 437,883,097
Basic weighted average shares outstanding (in shares)									242,599,923		251,766,382		267,794,786
Net Income per share - Basic (in dollars per share)	$ 0.58	$ 0.48	$ (0.01)	$ 0.36	$ 0.39	$ 0.44	$ 0.42	$ 0.40	$ 1.41	[1]	$ 1.67	[1]	$ 1.64	[1]
Diluted Earnings Per Share
Allocation of Net Income used in basic computation									$ 342,598,693		$ 419,655,126		$ 437,883,097
Reallocation of undistributed earnings									14,232		21,104		21,007
Net Income available to common shareholders - Diluted									$ 342,612,925		$ 419,676,230		$ 437,904,104
Number of shares used in basic computation (in shares)									242,599,923		251,766,382		267,794,786
Additional weighted average dilutive common stock equivalents (in shares)									1,082,069		1,506,608		2,082,563
Diluted weighted average shares outstanding (in shares)									243,681,992		253,272,990		269,877,349
Net income per share - Diluted (in dollars per share)	$ 0.59	$ 0.48	$ (0.01)	$ 0.36	$ 0.39	$ 0.44	$ 0.42	$ 0.40	$ 1.41	[1]	$ 1.66	[1]	$ 1.62	[1]

[1] (1) Earnings Per Share has been adjusted to exclude the portion of net income allocated to participating securities as a result of share-based payment awards