Investment Securities - Unrealized Losses and Fair Value of Debt Securities Held to Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Fair Value
Less than Twelve Months	$ 65,687	$ 324,246
More than Twelve Months	51,231	323,080
Total	116,918	647,326
Unrealized Losses
Less than Twelve Months	(572)	(1,483)
More than Twelve Months	(7,766)	(10,448)
Total	(8,338)	(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	10,544	11,178
More than Twelve Months	20,022	32,397
Total	30,566	43,575
Unrealized Losses
Less than Twelve Months	(266)	(55)
More than Twelve Months	(279)	(474)
Total	(545)	(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)
Obligations of states and political subdivisions
Fair Value
Less than Twelve Months	10,544	11,178
More than Twelve Months	20,022	33,195
Total	30,566	44,373
Unrealized Losses
Less than Twelve Months	(266)	(55)
More than Twelve Months	(279)	(484)
Total	(545)	(539)
Residential mortgage-backed securities
Fair Value
Less than Twelve Months	37,394	307,885
More than Twelve Months	2,710	254,915
Total	40,104	562,800
Unrealized Losses
Less than Twelve Months	(305)	(1,387)
More than Twelve Months	(4)	(3,963)
Total	(309)	(5,350)
Trust preferred securities
Fair Value
Less than Twelve Months	0	0
More than Twelve Months	28,499	29,990
Total	28,499	29,990
Unrealized Losses
Less than Twelve Months	0	0
More than Twelve Months	(7,483)	(5,981)
Total	(7,483)	(5,981)
Corporate and other debt securities
Fair Value
Less than Twelve Months	17,749	0
More than Twelve Months	0	4,980
Total	17,749	4,980
Unrealized Losses
Less than Twelve Months	(1)	0
More than Twelve Months	0	(20)
Total	$ (1)	$ (20)