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	Jun. 30, 2014	Dec. 31, 2013
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	$ 33,121	$ 237,965
Less than 12 Months, Unrealized Losses	101	5,579
12 Months or Longer, Fair Value	27,034	5,977
12 Months or Longer, Unrealized Losses	1,366	3,964
Total, Fair Value	60,155	243,942
Total, Gross Unrealized Losses	1,467	9,543
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	67,611	230,366
Less than 12 Months, Gross Unrealized Losses	518	3,553
12 Months or Longer, Fair Value	23,550	2,824
12 Months or Longer, Gross Unrealized Losses	341	260
Total, Fair Value	91,161	233,190
Total, Gross Unrealized Losses	859	3,813
Available-for-sale Securities and Held-to-maturity Securities [Abstract]
Less than 12 Months, Fair Value	100,732	468,331
Less than 12 Months, Gross Unrealized Losses	619	9,132
12 Months or Longer, Fair Value	50,584	8,801
12 Months or Longer, Gross Unrealized Losses	1,707	4,224
Total, Fair Value	151,316	477,132
Total, Gross Unrealized Losses	2,326	13,356
State and municipal
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	14,351	17,318
Less than 12 Months, Gross Unrealized Losses	157	91
12 Months or Longer, Fair Value		184
12 Months or Longer, Gross Unrealized Losses		1
Total, Fair Value	14,351	17,502
Total, Gross Unrealized Losses	157	92
U.S. Government-sponsored mortgage-backed securities
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	53,260	213,048
Less than 12 Months, Gross Unrealized Losses	361	3,462
12 Months or Longer, Fair Value	23,550	2,640
12 Months or Longer, Gross Unrealized Losses	341	259
Total, Fair Value	76,810	215,688
Total, Gross Unrealized Losses	702	3,721
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	8,707	111,791
Less than 12 Months, Unrealized Losses	36	3,840
12 Months or Longer, Fair Value	20,501	583
12 Months or Longer, Unrealized Losses	420	56
Total, Fair Value	29,208	112,374
Total, Gross Unrealized Losses	456	3,896
U.S. Government-sponsored mortgage-backed securities
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	24,414	117,866
Less than 12 Months, Unrealized Losses	65	1,701
12 Months or Longer, Fair Value	5,769	2,683
12 Months or Longer, Unrealized Losses	177	272
Total, Fair Value	30,183	120,549
Total, Gross Unrealized Losses	242	1,973
Corporate obligations
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
12 Months or Longer, Fair Value	764	2,711
12 Months or Longer, Unrealized Losses	769	3,636
Total, Fair Value	764	2,711
Total, Gross Unrealized Losses	$ 769	$ 3,636