Recent Accounting Standards (Narrative) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Cumulative effect adjustment	$ 1,805,586	$ 1,704,496	$ 1,672,020	$ 1,683,026	$ 1,622,447	$ 1,538,049	$ 1,483,799	$ 1,441,339
Decrease to deferred income tax liability	95,221			37,814
Decrease to retained earnings	$ 3,085,204			2,921,448
Accounting Standards Update 2016-13 [Member] | Revision of Prior Period, Accounting Standards Update, Adjustment [Member]
Cumulative effect adjustment				(1,051)
Increase to allowance for credit losses				1,414
Decrease to deferred income tax liability				(363)
Decrease to retained earnings				$ (1,051)