Investment Securities - Age of Unrealized Losses and Fair Value of Related Securities Held to Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair Value
Less than Twelve Months	$ 37,894	$ 324,246
More than Twelve Months	31,100	323,080
Total	68,994	647,326
Unrealized Losses
Less than Twelve Months	(351)	(1,483)
More than Twelve Months	(7,374)	(10,448)
Total	(7,725)	(11,931)
U.S. government agency securities
Fair Value
Less than Twelve Months		5,183
More than Twelve Months		0
Total		5,183
Unrealized Losses
Less than Twelve Months		(41)
More than Twelve Months		0
Total		(41)
Obligations of states and state agencies
Fair Value
Less than Twelve Months	5,546	11,178
More than Twelve Months	0	32,397
Total	5,546	43,575
Unrealized Losses
Less than Twelve Months	(105)	(55)
More than Twelve Months	0	(474)
Total	(105)	(529)
Municipal bonds
Fair Value
Less than Twelve Months		0
More than Twelve Months		798
Total		798
Unrealized Losses
Less than Twelve Months		0
More than Twelve Months		(10)
Total		(10)
Total obligations of states and political subdivisions
Fair Value
Less than Twelve Months		11,178
More than Twelve Months		33,195
Total		44,373
Unrealized Losses
Less than Twelve Months		(55)
More than Twelve Months		(484)
Total		(539)
Residential mortgage-backed securities
Fair Value
Less than Twelve Months	21,599	307,885
More than Twelve Months	2,470	254,915
Total	24,069	562,800
Unrealized Losses
Less than Twelve Months	(245)	(1,387)
More than Twelve Months	(9)	(3,963)
Total	(254)	(5,350)
Trust preferred securities
Fair Value
Less than Twelve Months	0	0
More than Twelve Months	28,630	29,990
Total	28,630	29,990
Unrealized Losses
Less than Twelve Months	0	0
More than Twelve Months	(7,365)	(5,981)
Total	(7,365)	(5,981)
Corporate and other debt securities
Fair Value
Less than Twelve Months	10,749	0
More than Twelve Months	0	4,980
Total	10,749	4,980
Unrealized Losses
Less than Twelve Months	(1)	0
More than Twelve Months	0	(20)
Total	$ (1)	$ (20)