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, 2017	Dec. 31, 2016
Fair Value
Less than 12 Months	$ 187,271	$ 330,902
12 Months or Longer	3,990
Total	191,261	330,902
Gross Unrealized Losses
Less than 12 Months	4,030	9,674
12 Months or Longer	151
Total	4,181	9,674
Fair Value
Less than 12 Months	122,019	179,395
12 Months or Longer	4,910
Total	126,929	179,395
Gross Unrealized Losses
Less than 12 Months	2,085	3,802
12 Months or Longer	89
Total	2,174	3,802
Available-for-sale Securities and Held-to-maturity Securities [Abstract]
Less than 12 Months, Fair Value	309,290	510,297
12 Months or Longer, Fair Value	8,900
Total, Fair Value	318,190	510,297
Less than 12 Months, Gross Unrealized Losses	6,115	13,476
12 Months or Longer, Gross Unrealized Losses	240
Total, Gross Unrealized Losses	6,355	13,476
State and municipal
Fair Value
Less than 12 Months	56,404	126,593
12 Months or Longer	2,547
Total	58,951	126,593
Gross Unrealized Losses
Less than 12 Months	1,887	5,564
12 Months or Longer	118
Total	2,005	5,564
U.S. Government-sponsored mortgage-backed securities
Fair Value
Less than 12 Months	130,867	185,544
12 Months or Longer	1,443
Total	132,310	185,544
Gross Unrealized Losses
Less than 12 Months	2,143	3,071
12 Months or Longer	33
Total	2,176	3,071
Equity securities
Fair Value
Less than 12 Months		18,765
Total		18,765
Gross Unrealized Losses
Less than 12 Months		1,039
Total		1,039
U.S. Government-sponsored agency securities
Fair Value
Less than 12 Months	17,225
12 Months or Longer	4,910
Total	22,135
Gross Unrealized Losses
Less than 12 Months	293
12 Months or Longer	89
Total	382
U.S. Government-sponsored agency securities
Fair Value
Less than 12 Months		19,121
Total		19,121
Gross Unrealized Losses
Less than 12 Months		479
Total		479
State and municipal
Fair Value
Less than 12 Months	25,198	50,897
12 Months or Longer
Total	25,198	50,897
Gross Unrealized Losses
Less than 12 Months	747	1,796
12 Months or Longer
Total	747	1,796
U.S. Government-sponsored mortgage-backed securities
Fair Value
Less than 12 Months	79,596	109,377
12 Months or Longer
Total	79,596	109,377
Gross Unrealized Losses
Less than 12 Months	1,045	1,527
12 Months or Longer
Total	$ 1,045	$ 1,527