Derivative Financial Instruments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Junior subordinated debentures	$ 51,578		$ 51,578		$ 43,136
Notional amount	1,534,520		1,534,520		1,481,109
Short term advances and brokered CD's	996,500		996,500		1,021,500
Derivative instruments	(25,803)		(25,803)		(59,668)
Customer [Member]
Derivative instruments	114,800		114,800		62,800
Bank [Member]
Derivative instruments	114,800		114,800		62,800
Customer and Bank [Member]
Derivative instruments	229,700		229,700		125,600
Cash Flow Hedging [Member]
Amount reclassified from accumulated other comprehensive loss to interest expense	2,600	$ 1,400	7,900	$ 2,100
Amount to be reclassified from the accumulated comprehensive income (loss) into earnings			10,500
Not Designated as Hedging Instrument [Member]
Notional amount	229,700		229,700		143,600
Designated as Hedging Instrument [Member]
Notional amount	308,400		308,400		316,100
Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member]
Notional amount	996,500		996,500		1,021,500
Interest Rate Swap [Member]
Notional amount	308,400		308,400		316,100
Interest Rate Swap [Member] | Not Designated as Hedging Instrument [Member]
Notional amount	114,835		114,835		80,779
Derivative instruments	(3,225)		(3,225)		(6,998)
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member]
Notional amount	641,500		641,500		1,021,500
Derivative instruments	(14,675)		$ (14,675)		(25,300)
Floating Rate Junior Subordinated Debentures [Member]
Amount of hedged item					18,000
Junior subordinated debentures					$ 61,900
Gain (loss) on termination of swaps	$ (4,700)