Derivative Financial Instruments - Interest Rate Swaps Not Designated as Hedges (Details) - Interest rate swap - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Gross gains and losses on derivative assets and liabilities recorded in Consolidated Statements of Income
Net gains (losses)	$ 0	$ 0
Derivative cash pledged	36,500		$ 18,100
Not designated as hedging
Derivative Financial Instruments
Notional amount	650,200		580,800
Variable rate, commercial loans that are supported by the interest rate swap contracts	325,100		290,400
Non-interest income
Gross gains and losses on derivative assets and liabilities recorded in Consolidated Statements of Income
Gross gains	23,478	3,713
Non-interest expense
Gross gains and losses on derivative assets and liabilities recorded in Consolidated Statements of Income
Gross (losses)	(23,478)	$ (3,713)
Other assets
Fair values of derivative assets and liabilities recorded in consolidated balance sheets
Fair value recorded in other assets	35,832		12,354
Other liabilities
Fair values of derivative assets and liabilities recorded in consolidated balance sheets
Fair value recorded in other liabilities	$ 35,832		$ 12,354