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Derivative Financial Instruments - Interest Rate Swaps Not Designated as Hedges (Details) - Interest rate swap - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Gross gains and losses on derivative assets and liabilities recorded in Consolidated Statements of Income
Net gains (losses)	$ 0	$ 0	$ 0	$ 0
Derivative cash pledged	38,800		38,800		$ 18,100
Not designated as hedging
Derivative Financial Instruments
Notional amount	685,200		685,200		580,800
Variable rate, commercial loans that are supported by the interest rate swap contracts	342,600		342,600		290,400
Non-interest income
Gross gains and losses on derivative assets and liabilities recorded in Consolidated Statements of Income
Gross gains	2,861	73	26,339	164
Non-interest expense
Gross gains and losses on derivative assets and liabilities recorded in Consolidated Statements of Income
Gross (losses)	(2,861)	$ (73)	(26,339)	$ (164)
Other assets
Fair values of derivative assets and liabilities recorded in consolidated balance sheets
Fair value recorded in other assets	38,693		38,693		12,354
Other liabilities
Fair values of derivative assets and liabilities recorded in consolidated balance sheets
Fair value recorded in other liabilities	$ 38,693		$ 38,693		$ 12,354