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, 2017	Dec. 31, 2016
Fair Value
Less than 12 Months	$ 293,519	$ 330,902
12 Months or Longer
Total	293,519	330,902
Gross Unrealized Losses
Less than 12 Months	7,102	9,674
12 Months or Longer
Total	7,102	9,674
Fair Value
Less than 12 Months	167,438	179,395
12 Months or Longer
Total	167,438	179,395
Gross Unrealized Losses
Less than 12 Months	3,375	3,802
12 Months or Longer
Total	3,375	3,802
Available-for-sale Securities and Held-to-maturity Securities [Abstract]
Less than 12 Months, Fair Value	460,957	510,297
12 Months or Longer, Fair Value
Total, Fair Value	460,957	510,297
Less than 12 Months, Gross Unrealized Losses	10,477	13,476
12 Months or Longer, Gross Unrealized Losses
Total, Gross Unrealized Losses	10,477	13,476
State and municipal
Fair Value
Less than 12 Months	109,641	126,593
12 Months or Longer
Total	109,641	126,593
Gross Unrealized Losses
Less than 12 Months	4,153	5,564
12 Months or Longer
Total	4,153	5,564
U.S. Government-sponsored mortgage-backed securities
Fair Value
Less than 12 Months	183,878	185,544
12 Months or Longer
Total	183,878	185,544
Gross Unrealized Losses
Less than 12 Months	2,949	3,071
12 Months or Longer
Total	2,949	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	22,160
12 Months or Longer
Total	22,160
Gross Unrealized Losses
Less than 12 Months	458
12 Months or Longer
Total	458
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	36,582	50,897
12 Months or Longer
Total	36,582	50,897
Gross Unrealized Losses
Less than 12 Months	1,386	1,796
12 Months or Longer
Total	1,386	1,796
U.S. Government-sponsored mortgage-backed securities
Fair Value
Less than 12 Months	108,696	109,377
12 Months or Longer
Total	108,696	109,377
Gross Unrealized Losses
Less than 12 Months	1,531	1,527
12 Months or Longer
Total	$ 1,531	$ 1,527