Commitments, Off-Balance Sheet Arrangements, Legal Proceedings and Regulatory Matters, Summary of Lending Related and Other Commitments (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of lending-related and other commitments [Line Items]
Lending related commitments, fair value	$ 0	$ 0
Commitments to extend credit, excluding commitments to originate residential mortgage loans held for sale
Summary of lending-related and other commitments
Lending related commitments	8,481,563	8,027,187
Commercial Letters Of Credit
Summary of lending-related and other commitments
Lending related commitments	12,456	11,886
Standby Letters of Credit
Summary of lending-related and other commitments
Lending related commitments	253,857	235,361
Standby letters of credit, fair value	$ 2,000	$ 2,000