Summary of Significant Accounting Policies - Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands		3 Months Ended			9 Months Ended
	Jan. 01, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2020		Sep. 30, 2019
Cash Transactions:
Interest paid					$ 179,163		$ 216,261
Income taxes paid, net					89,858		61,238
Operating lease payments					10,077		10,193
Noncash Transactions:
Loans charged-off to the allowance for credit losses		$ 15,029	$ 6,780		35,724		21,328
Loans foreclosed upon and transferred to other real estate owned					3,435		16,870
Loans foreclosed upon and transferred to other assets					25		93
Fixed assets transferred to other real estate owned					0		5,126
Available-for-sale securities transferred to held-to-maturity portfolio				$ 179,800	873,613		0
Right of use assets recognized during the period in exchange for lease obligations	$ 79,900				$ 5,269	[1]	$ 82,856	[1]

[1] (1) Includes $79.9 million recognized upon initial adoption of ASU 2016-02 on January 1, 2019.