Current Accounting Developments and Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Mar. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for loan losses	$ 557,003		$ 358,287	$ 317,894
Retained earnings	$ 3,695,759		$ 3,689,377
ASU 2016-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for loan losses		$ 125,200
Retained earnings		98,000
ASU 2016-13 | Unfunded Credit Commitments
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for loan losses		$ 10,500