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, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	$ 21,335	$ 237,965
Less than 12 Months, Unrealized Losses	105	5,579
12 Months or Longer, Fair Value	20,114	5,977
12 Months or Longer, Unrealized Losses	1,101	3,964
Total, Fair Value	41,449	243,942
Total, Gross Unrealized Losses	1,206	9,543
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	66,479	230,366
Less than 12 Months, Gross Unrealized Losses	751	3,553
12 Months or Longer, Fair Value	18,639	2,824
12 Months or Longer, Gross Unrealized Losses	294	260
Total, Fair Value	85,118	233,190
Total, Gross Unrealized Losses	1,045	3,813
Available-for-sale Securities and Held-to-maturity Securities [Abstract]
Less than 12 Months, Fair Value	87,814	468,331
Less than 12 Months, Gross Unrealized Losses	856	9,132
12 Months or Longer, Fair Value	38,753	8,801
12 Months or Longer, Gross Unrealized Losses	1,395	4,224
Total, Fair Value	126,567	477,132
Total, Gross Unrealized Losses	2,251	13,356
State and municipal
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	8,475	17,318
Less than 12 Months, Gross Unrealized Losses	64	91
12 Months or Longer, Fair Value		184
12 Months or Longer, Gross Unrealized Losses
Total, Fair Value	8,475	17,502
Total, Gross Unrealized Losses	64	91
U.S. Government-sponsored mortgage-backed securities
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	58,004	213,048
Less than 12 Months, Gross Unrealized Losses	687	3,462
12 Months or Longer, Fair Value	18,639	2,640
12 Months or Longer, Gross Unrealized Losses	294	260
Total, Fair Value	76,643	215,688
Total, Gross Unrealized Losses	981	3,722
U.S. Treasury
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value		4,875
Less than 12 Months, Unrealized Losses		21
Total, Fair Value		4,875
Total, Gross Unrealized Losses		21
U.S. Government-sponsored agency securities
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value		3,433
Less than 12 Months, Unrealized Losses		17
Total, Fair Value		3,433
Total, Gross Unrealized Losses		17
State and municipal
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	3,239	111,791
Less than 12 Months, Unrealized Losses	5	3,840
12 Months or Longer, Fair Value	13,678	583
12 Months or Longer, Unrealized Losses	201	56
Total, Fair Value	16,917	112,374
Total, Gross Unrealized Losses	206	3,896
U.S. Government-sponsored mortgage-backed securities
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	18,096	117,866
Less than 12 Months, Unrealized Losses	100	1,701
12 Months or Longer, Fair Value	5,615	2,683
12 Months or Longer, Unrealized Losses	183	272
Total, Fair Value	23,711	120,549
Total, Gross Unrealized Losses	283	1,973
Corporate obligations
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
12 Months or Longer, Fair Value	821	2,711
12 Months or Longer, Unrealized Losses	717	3,636
Total, Fair Value	821	2,711
Total, Gross Unrealized Losses	$ 717	$ 3,636