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	Mar. 31, 2020	Dec. 31, 2019
Fair Value
Less than 12 Months	$ 51,315	$ 203,946
12 Months or Longer	0	20,796
Total	51,315	224,742
Gross Unrealized Losses
Less than 12 Months	407	2,133
12 Months or Longer	0	78
Total	407	2,211
Fair Value
Less than 12 Months	6,815	150,216
12 Months or Longer	0	20,458
Total	6,815	170,674
Gross Unrealized Losses
Less than 12 Months	28	475
12 Months or Longer	0	70
Total	28	545
Less than 12 Months, Fair Value	58,130	354,162
12 Months or Longer, Fair Value	0	41,254
Total, Fair Value	58,130	395,416
Less than 12 Months, Gross Unrealized Losses	435	2,608
12 Months or Longer, Gross Unrealized Losses	0	148
Total, Gross Unrealized Losses	435	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	34,304	76,273
12 Months or Longer	0	0
Total	34,304	76,273
Gross Unrealized Losses
Less than 12 Months	306	807
12 Months or Longer	0	0
Total	306	807
Fair Value
Less than 12 Months	6,815	22,947
12 Months or Longer	0	0
Total	6,815	22,947
Gross Unrealized Losses
Less than 12 Months	28	107
12 Months or Longer	0	0
Total	28	107
U.S. Government-sponsored mortgage-backed securities
Fair Value
Less than 12 Months	17,011	127,673
12 Months or Longer	0	20,796
Total	17,011	148,469
Gross Unrealized Losses
Less than 12 Months	101	1,326
12 Months or Longer	0	78
Total	$ 101	1,404
Fair Value
Less than 12 Months		124,253
12 Months or Longer		7,991
Total		132,244
Gross Unrealized Losses
Less than 12 Months		364
12 Months or Longer		37
Total		$ 401