Investment Securities Held to Maturity (Details) $ in Thousands	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Mar. 31, 2015 USD ($)	Mar. 31, 2014 USD ($)
Schedule of Held-to-maturity Securities [Line Items]
Held-to-Maturity	$ 315,284	$ 320,611	$ 305,175
Held-to-Maturity Securities, at Fair Value	324,337	325,930	312,500	$ 312,500
Gross Unrealized Gains	9,061	5,487	7,451
Gross Unrealized Losses	8	168	126
Held-To-Maturity Securities, Pledged as Collateral	299,767	299,767	285,132
Maturities of Debt Securities at Amortized Cost
Within One Year	38,848
From 1 - 5 Years	139,795
From 5 - 10 Years	131,614
Over 10 Years	5,027
Maturities of Debt Securities, at Fair Value
Within One Year	38,909
From 1 - 5 Years	143,584
From 5 - 10 Years	136,679
Over 10 Years	5,165
Securities in a Continuous Loss Position, at Fair Value
Less than 12 Months	4,293	8,302	0
12 Months or Longer	658	15,918	16,010
Total	$ 4,951	$ 24,220	$ 16,010
Number of Securities in a Continuous Loss Position, in number of securities	8	62	592
Unrealized Losses on Securities in a Continuous Loss Position
Less than 12 Months	$ 6	$ 104	$ 0
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2	64	126
Total	8	168	126
State and Municipal Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-Maturity	224,831	226,053	195,951
Held-to-Maturity Securities, at Fair Value	231,598	230,621	200,578
Gross Unrealized Gains	6,769	4,619	4,753
Gross Unrealized Losses	2	51	126
Maturities of Debt Securities at Amortized Cost
Within One Year	38,848
From 1 - 5 Years	88,146
From 5 - 10 Years	93,810
Over 10 Years	4,027
Maturities of Debt Securities, at Fair Value
Within One Year	38,909
From 1 - 5 Years	90,744
From 5 - 10 Years	97,780
Over 10 Years	4,165
Securities in a Continuous Loss Position, at Fair Value
Less than 12 Months	648	2,302	0
12 Months or Longer	658	11,764	16,010
Total	$ 1,306	$ 14,066	$ 16,010
Number of Securities in a Continuous Loss Position, in number of securities	7	54	585
Unrealized Losses on Securities in a Continuous Loss Position
Less than 12 Months	$ 0	$ 11	$ 0
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2	40	126
Total	2	51	126
Mortgage-Backed Securities - Residential [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-Maturity	89,453	93,558	108,224
Held-to-Maturity Securities, at Fair Value	91,739	94,309	110,922
Gross Unrealized Gains	2,292	868	2,698
Gross Unrealized Losses	6	117	0
Maturities of Debt Securities at Amortized Cost
Within One Year	0
From 1 - 5 Years	51,649
From 5 - 10 Years	37,804
Over 10 Years	0
Maturities of Debt Securities, at Fair Value
Within One Year	0
From 1 - 5 Years	52,840
From 5 - 10 Years	38,899
Over 10 Years	0
Securities in a Continuous Loss Position, at Fair Value
Less than 12 Months	3,645	6,000	0
12 Months or Longer	0	4,154	0
Total	$ 3,645	$ 10,154	$ 0
Number of Securities in a Continuous Loss Position, in number of securities	1	8	7
Unrealized Losses on Securities in a Continuous Loss Position
Less than 12 Months	$ 6	$ 93	$ 0
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	24	0
Total	6	117	0
Mortgage-Backed Securities - Residential [Member] | U.S. Government Agency Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-Maturity	3,700	3,800	29,900
Held-to-Maturity Securities, at Fair Value	3,800	3,900	30,600
Mortgage-Backed Securities - Residential [Member] | US Government-sponsored Enterprises Debt Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-Maturity	85,800	89,800	78,300
Held-to-Maturity Securities, at Fair Value	87,900	90,500	80,300
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
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0	0
Total	$ 0	$ 0	$ 0