Investment Securities - Investments' Gross Unrealized Losses and Fair Value Aggregated by Investment Category and Length of Time in Continuous Unrealized Loss Position (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Fair Value
Less than 12 Months	$ 38,984	$ 203,946
12 Months or Longer	0	20,796
Total	38,984	224,742
Gross Unrealized Losses
Less than 12 Months	165	2,133
12 Months or Longer	0	78
Total	165	2,211
Fair Value
Less than 12 Months	12,831	150,216
12 Months or Longer	0	20,458
Total	12,831	170,674
Gross Unrealized Losses
Less than 12 Months	74	475
12 Months or Longer	0	70
Total	74	545
Less than 12 Months, Fair Value	51,815	354,162
12 Months or Longer, Fair Value	0	41,254
Total, Fair Value	51,815	395,416
Less than 12 Months, Gross Unrealized Losses	239	2,608
12 Months or Longer, Gross Unrealized Losses	0	148
Total, Gross Unrealized Losses	239	2,756
U.S. Government-sponsored agency securities
Fair Value
Less than 12 Months		3,016
12 Months or Longer		12,467
Total		15,483
Gross Unrealized Losses
Less than 12 Months		4
12 Months or Longer		33
Total		37
State and municipal
Fair Value
Less than 12 Months	23,745	76,273
12 Months or Longer	0	0
Total	23,745	76,273
Gross Unrealized Losses
Less than 12 Months	138	807
12 Months or Longer	0	0
Total	138	807
Fair Value
Less than 12 Months	2,633	22,947
12 Months or Longer	0	0
Total	2,633	22,947
Gross Unrealized Losses
Less than 12 Months	43	107
12 Months or Longer	0	0
Total	43	107
U.S. Government-sponsored mortgage-backed securities
Fair Value
Less than 12 Months	15,239	127,673
12 Months or Longer	0	20,796
Total	15,239	148,469
Gross Unrealized Losses
Less than 12 Months	27	1,326
12 Months or Longer	0	78
Total	27	1,404
Fair Value
Less than 12 Months	10,198	124,253
12 Months or Longer	0	7,991
Total	10,198	132,244
Gross Unrealized Losses
Less than 12 Months	31	364
12 Months or Longer	0	37
Total	$ 31	$ 401