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	Sep. 30, 2017	Dec. 31, 2016
Fair Value
Less than 12 Months	$ 230,302	$ 330,902
12 Months or Longer	29,842
Total	260,144	330,902
Gross Unrealized Losses
Less than 12 Months	2,753	9,674
12 Months or Longer	1,210
Total	3,963	9,674
Fair Value
Less than 12 Months	103,645	179,395
12 Months or Longer	18,483
Total	122,128	179,395
Gross Unrealized Losses
Less than 12 Months	1,292	3,802
12 Months or Longer	406
Total	1,698	3,802
Available-for-sale Securities and Held-to-maturity Securities [Abstract]
Less than 12 Months, Fair Value	333,947	510,297
12 Months or Longer, Fair Value	48,325
Total, Fair Value	382,272	510,297
Less than 12 Months, Gross Unrealized Losses	4,045	13,476
12 Months or Longer, Gross Unrealized Losses	1,616
Total, Gross Unrealized Losses	5,661	13,476
State and municipal
Fair Value
Less than 12 Months	76,469	126,593
12 Months or Longer	21,693
Total	98,162	126,593
Gross Unrealized Losses
Less than 12 Months	959	5,564
12 Months or Longer	1,047
Total	2,006	5,564
U.S. Government-sponsored mortgage-backed securities
Fair Value
Less than 12 Months	153,833	185,544
12 Months or Longer	8,149
Total	161,982	185,544
Gross Unrealized Losses
Less than 12 Months	1,794	3,071
12 Months or Longer	163
Total	1,957	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	9,941	19,121
12 Months or Longer	12,267
Total	22,208	19,121
Gross Unrealized Losses
Less than 12 Months	78	479
12 Months or Longer	233
Total	311	479
State and municipal
Fair Value
Less than 12 Months	18,754	50,897
12 Months or Longer	6,216
Total	24,970	50,897
Gross Unrealized Losses
Less than 12 Months	402	1,796
12 Months or Longer	173
Total	575	1,796
U.S. Government-sponsored mortgage-backed securities
Fair Value
Less than 12 Months	74,950	109,377
12 Months or Longer
Total	74,950	109,377
Gross Unrealized Losses
Less than 12 Months	812	1,527
12 Months or Longer
Total	$ 812	$ 1,527