Investment Securities - Unrealized Losses and Fair Value of Debt Securities Held to Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value
Less than Twelve Months	$ 250,057	$ 324,246
More than Twelve Months	31,272	323,080
Total	281,329	647,326
Unrealized Losses
Less than Twelve Months	(1,101)	(1,483)
More than Twelve Months	(7,398)	(10,448)
Total	(8,499)	(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	5,493	11,178
More than Twelve Months	0	32,397
Total	5,493	43,575
Unrealized Losses
Less than Twelve Months	(176)	(55)
More than Twelve Months	0	(474)
Total	(176)	(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	5,493	11,178
More than Twelve Months	0	33,195
Total	5,493	44,373
Unrealized Losses
Less than Twelve Months	(176)	(55)
More than Twelve Months	0	(484)
Total	(176)	(539)
Residential mortgage-backed securities
Fair Value
Less than Twelve Months	237,070	307,885
More than Twelve Months	2,677	254,915
Total	239,747	562,800
Unrealized Losses
Less than Twelve Months	(919)	(1,387)
More than Twelve Months	(5)	(3,963)
Total	(924)	(5,350)
Trust preferred securities
Fair Value
Less than Twelve Months	0	0
More than Twelve Months	28,595	29,990
Total	28,595	29,990
Unrealized Losses
Less than Twelve Months	0	0
More than Twelve Months	(7,393)	(5,981)
Total	(7,393)	(5,981)
Corporate and other debt securities
Fair Value
Less than Twelve Months	7,494	0
More than Twelve Months	0	4,980
Total	7,494	4,980
Unrealized Losses
Less than Twelve Months	(6)	0
More than Twelve Months	0	(20)
Total	$ (6)	$ (20)