Investment Securities Held to Maturity (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity	$ 251,456	$ 239,803	$ 200,607
Held-to-Maturity Securities, at Fair Value	259,562	248,252	207,779
Gross Unrealized Gains	8,140	8,512	7,432
Gross Unrealized Losses	34	63	260
Held-To-Maturity Securities, Pledged as Collateral	250,456	238,803	199,607
Maturities of Debt Securities at Amortized Cost
Within One Year	46,701
From 1 - 5 Years	123,160
From 5 - 10 Years	75,122
Over 10 Years	6,473
Maturities of Debt Securities, at Fair Value
Within One Year	46,740
From 1 - 5 Years	125,061
From 5 - 10 Years	80,919
Over 10 Years	6,842
Securities in a Continuous Loss Position, at Fair Value
Less than 12 Months	8,794	21,583	45,423
12 Months or Longer	173	503	0
Total	8,967	22,086	45,423
Number of Securities in a Continuous Loss Position, in number of securities	33	61	51
Unrealized Losses on Securities in a Continuous Loss Position
Less than 12 Months	34	62	260
12 Months or Longer	0	1	0
Total	34	63	260
State and Municipal Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity	198,858	183,373	159,790
Held-to-Maturity Securities, at Fair Value	206,141	191,196	167,109
Gross Unrealized Gains	7,317	7,886	7,415
Gross Unrealized Losses	34	63	96
Maturities of Debt Securities at Amortized Cost
Within One Year	46,701
From 1 - 5 Years	71,562
From 5 - 10 Years	75,122
Over 10 Years	5,473
Maturities of Debt Securities, at Fair Value
Within One Year	46,740
From 1 - 5 Years	72,640
From 5 - 10 Years	80,919
Over 10 Years	5,842
Securities in a Continuous Loss Position, at Fair Value
Less than 12 Months	8,794	21,583	11,719
12 Months or Longer	173	503	0
Total	8,967	22,086	11,719
Number of Securities in a Continuous Loss Position, in number of securities	33	61	33
Unrealized Losses on Securities in a Continuous Loss Position
Less than 12 Months	34	62	96
12 Months or Longer	0	1	0
Total	34	63	96
Mortgage-Backed Securities - Residential [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity	51,598	55,430	39,817
Held-to-Maturity Securities, at Fair Value	52,421	56,056	39,670
Gross Unrealized Gains	823	626	17
Gross Unrealized Losses	0	0	164
Maturities of Debt Securities at Amortized Cost
Within One Year	0
From 1 - 5 Years	51,598
From 5 - 10 Years	0
Over 10 Years	0
Maturities of Debt Securities, at Fair Value
Within One Year	0
From 1 - 5 Years	52,421
From 5 - 10 Years	0
Over 10 Years	0
Securities in a Continuous Loss Position, at Fair Value
Less than 12 Months	0	0	33,704
12 Months or Longer	0	0	0
Total	0	0	33,704
Number of Securities in a Continuous Loss Position, in number of securities	0	0	18
Unrealized Losses on Securities in a Continuous Loss Position
Less than 12 Months	0	0	164
12 Months or Longer	0	0	0
Total	0	0	164
Corporate and Other Debt Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity	1,000	1,000	1,000
Held-to-Maturity Securities, at Fair Value	1,000	1,000	1,000
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	0	0	0
Maturities of Debt Securities at Amortized Cost
Within One Year	0
From 1 - 5 Years	0
From 5 - 10 Years	0
Over 10 Years	1,000
Maturities of Debt Securities, at Fair Value
Within One Year	0
From 1 - 5 Years	0
From 5 - 10 Years	0
Over 10 Years	1,000
Securities in a Continuous Loss Position, at Fair Value
Less than 12 Months	0	0	0
12 Months or Longer	0	0	0
Total	0	0	0
Number of Securities in a Continuous Loss Position, in number of securities	0	0	0
Unrealized Losses on Securities in a Continuous Loss Position
Less than 12 Months	0	0	0
12 Months or Longer	0	0	0
Total	0	0	0
US Government-sponsored Enterprises Debt Securities [Member] | Mortgage-Backed Securities - Residential [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity	51,600		39,800
Held-to-Maturity Securities, at Fair Value	$ 52,400		$ 39,700