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, 2015	Dec. 31, 2014
Fair Value
Less than 12 Months	$ 111,070	$ 3,442
12 Months or Longer	2,212	15,297
Total	113,282	18,739
Gross Unrealized Losses
Less than 12 Months	1,814	20
12 Months or Longer	97	230
Total	1,911	250
Fair Value
Less than 12 Months	105,854	14,910
12 Months or Longer	14,222	38,741
Total	120,076	53,651
Gross Unrealized Losses
Less than 12 Months	1,754	178
12 Months or Longer	274	430
Total	2,028	608
Available-for-sale Securities and Held-to-maturity Securities [Abstract]
Less than 12 Months, Fair Value	216,924	18,352
12 Months or Longer, Fair Value	16,434	54,038
Total, Fair Value	233,358	72,390
Less than 12 Months, Gross Unrealized Losses	3,568	198
12 Months or Longer, Gross Unrealized Losses	371	660
Total, Gross Unrealized Losses	3,939	858
State and municipal
Fair Value
Less than 12 Months	$ 77,987	1,256
12 Months or Longer		9,850
Total	$ 77,987	11,106
Gross Unrealized Losses
Less than 12 Months	$ 1,707	7
12 Months or Longer		116
Total	$ 1,707	123
U.S. Government-sponsored mortgage-backed securities
Fair Value
Less than 12 Months	33,083	2,186
12 Months or Longer	2,212	5,447
Total	35,295	7,633
Gross Unrealized Losses
Less than 12 Months	107	13
12 Months or Longer	97	114
Total	204	127
State and municipal
Fair Value
Less than 12 Months	51,644	5,119
12 Months or Longer		250
Total	51,644	5,369
Gross Unrealized Losses
Less than 12 Months	1,262	$ 96
12 Months or Longer
Total	1,262	$ 96
U.S. Government-sponsored mortgage-backed securities
Fair Value
Less than 12 Months	54,210	9,791
12 Months or Longer	14,222	38,491
Total	68,432	48,282
Gross Unrealized Losses
Less than 12 Months	492	82
12 Months or Longer	274	430
Total	$ 766	$ 512