Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Earnings Per Share) (Details) - USD ($) $ 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
Numerator:
Net income	$ 438,111	$ 416,398	$ 348,620	$ 203,711	$ 335,798	$ 273,104	$ 241,041	$ 166,757	$ 1,406,839	$ 1,016,700	$ 1,022,023
Less: earnings distributed to participating securities									(1,106)	(1,228)	(1,208)
Less: undistributed earnings allocated to participating securities									(11,348)	(9,143)	(9,984)
Numerator for basic earnings per share									1,394,385	1,006,329	1,010,831
Add back: undistributed earnings allocated to participating securities									11,348	9,143	9,984
Less: undistributed earnings reallocated to participating securities									(11,312)	(9,117)	(9,939)
Numerator for diluted earnings per share									$ 1,394,421	$ 1,006,355	$ 1,010,876