Investment (Held-to-Maturity) Securities (Details) (USD $)	Mar. 31, 2013		Dec. 31, 2012		Mar. 31, 2012		Sep. 30, 2011
Schedule of Investment (Held-to-Maturity) Securities [Line Items]
Investment Securities, Amortized Cost	$ 585,378,000		$ 494,493,000		$ 417,405,000
Investments Securities, Carrying Value	589,271,000	[1]	499,534,000	[2]	427,259,000	[3]
Investment Securities, Fair Value	615,194,000		528,458,000		451,443,000
Investment Securities, Gross Unrealized Gain	26,554,000	[4]	29,427,000	[4]	24,729,000	[4]
Investment Securities, Gross Unrealized Loss	(631,000)	[4]	(503,000)	[4]	(545,000)	[4]
Investment Securities, Debt Maturities, Net Carrying Value [Abstract]
Investment Securities, Debt Maturities, Net Carrying Value	589,271,000
Investment Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Investment Securities, Debt Maturities, Fair Value	615,194,000
Investment Securities, Debt Maturities, Nominal Yield [Abstract]
Investment Securities, Debt Maturities, Nominal Yield	3.28%
Investment Securities, Pledged as Collateral [Abstract]
Investment Securities, Pledged as Collateral, Carrying Value	112,990,000		117,346,000		188,519,000
Investment Securities, Pledged as Collateral, Fair Value	118,054,000		121,647,000		192,844,000
Investment Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Investment Securities, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	77		67		4
Investment Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Investment Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	142,630,000		93,649,000		46,287,000
Investment Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0		0		0
Investment Securities, Continuous Unrealized Loss Position, Fair Value	142,630,000		93,649,000		46,287,000
Investment Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Investment Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	631,000		503,000		545,000
Investment Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	0		0		0
Investment Securities, Continuous Unrealized Loss Position, Aggregate Losses	631,000		503,000		545,000
Other than Temporary Impairment Losses, Investment Securities, Portion Recognized in Earnings, Net, Qualitative Disclosures, Lowest Current Credit Rating [Abstract]
Investment Securities, Portfolio Concentration US Govt or GSE Securities Not Rated, Carrying Value	72,968,000	[5]
Investment Securities, Portfolio Concentration US Govt or GSE Securities Not Rated, Fair Value	76,851,000	[5]
Investment Securities, Portfolio Concentration Rated AAA to AA, Carrying Value	428,254,000
Investment Securities, Portfolio Concentration Rated AAA to AA, Fair Value	447,952,000
Investment Securities, Portfolio Concentration Rated A to BBB, Carrying Value	25,960,000
Investment Securities, Portfolio Concentration Rated A to BBB, Fair Value	26,487,000
Investment Securities, Portfolio Concentration Rated Below Investment Grade, Carrying Value	0
Investment Securities, Portfolio Concentration Rated Below Investment Grade, Fair Value	0
Investment Securities, Portfolio Concentration Not Rated, Carrying Value	62,089,000
Investment Securities, Portfolio Concentration Not Rated, Fair Value	63,904,000
Fixed Maturity Securities [Member]
Investment Securities, Debt Maturities, Net Carrying Value [Abstract]
Investment Securities, Debt Maturities, Less than One Year, Net Carrying Value	36,370,000
Investment Securities, Debt Maturities, One to Five Years, Net Carrying Value	233,525,000
Investment Securities, Debt Maturities, Six to Ten Years, Net Carrying Value	143,795,000
Investment Securities, Debt Maturities, Over Ten Years, Net Carrying Value	102,613,000
Investment Securities, Debt Maturities, Net Carrying Value	516,303,000
Investment Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Investment Securities, Debt Maturities, Less Than One Year, Fair Value	36,582,000
Investment Securities, Debt Maturities, One to Five Years, Fair Value	236,528,000
Investment Securities, Debt Maturities, Six to Ten Years, Fair Value	147,255,000
Investment Securities, Debt Maturities, Over Ten Years, Fair Value	117,978,000
Investment Securities, Debt Maturities, Fair Value	538,343,000
Investment Securities, Debt Maturities, Nominal Yield [Abstract]
Investment Securities, Debt Maturities, Less Than One Year, Nominal Yield	4.24%
Investment Securities, Debt Maturities, One to Five Years, Nominal Yield	2.18%
Investment Securities, Debt Maturities, Six to Ten Years, Nominal Yield	2.94%
Investment Securities, Debt Maturities, Over Ten Years, Nominal Yield	6.30%
Investment Securities, Debt Maturities, Nominal Yield	3.36%
Investment Securities, Debt Maturities, Weighted Average Maturity	5.77	[6]
Municipal and Other Tax-exempt Securities [Member]
Schedule of Investment (Held-to-Maturity) Securities [Line Items]
Investment Securities, Amortized Cost	339,003,000		232,700,000		130,919,000
Investments Securities, Carrying Value	339,003,000	[1]	232,700,000	[2]	130,919,000	[3]
Investment Securities, Fair Value	341,940,000		235,940,000		135,314,000
Investment Securities, Gross Unrealized Gain	3,518,000	[4]	3,723,000	[4]	4,402,000	[4]
Investment Securities, Gross Unrealized Loss	(581,000)	[4]	(483,000)	[4]	(7,000)	[4]
Investment Securities, Debt Maturities, Net Carrying Value [Abstract]
Investment Securities, Debt Maturities, Less than One Year, Net Carrying Value	26,682,000
Investment Securities, Debt Maturities, One to Five Years, Net Carrying Value	201,547,000
Investment Securities, Debt Maturities, Six to Ten Years, Net Carrying Value	108,631,000
Investment Securities, Debt Maturities, Over Ten Years, Net Carrying Value	2,143,000
Investment Securities, Debt Maturities, Net Carrying Value	339,003,000
Investment Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Investment Securities, Debt Maturities, Less Than One Year, Fair Value	26,814,000
Investment Securities, Debt Maturities, One to Five Years, Fair Value	203,487,000
Investment Securities, Debt Maturities, Six to Ten Years, Fair Value	109,333,000
Investment Securities, Debt Maturities, Over Ten Years, Fair Value	2,306,000
Investment Securities, Debt Maturities, Fair Value	341,940,000
Investment Securities, Debt Maturities, Nominal Yield [Abstract]
Investment Securities, Debt Maturities, Less Than One Year, Nominal Yield	4.25%	[7]
Investment Securities, Debt Maturities, One to Five Years, Nominal Yield	1.71%	[7]
Investment Securities, Debt Maturities, Six to Ten Years, Nominal Yield	2.09%	[7]
Investment Securities, Debt Maturities, Over Ten Years, Nominal Yield	6.50%	[7]
Investment Securities, Debt Maturities, Nominal Yield	2.06%	[7]
Investment Securities, Debt Maturities, Effective tax rate for nominal yield calculation	39.00%
Investment Securities, Debt Maturities, Weighted Average Maturity	3.94	[6]
Investment Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Investment Securities, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	63		53		2
Investment Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Investment Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	141,778,000		92,768,000		619,000
Investment Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0		0		0
Investment Securities, Continuous Unrealized Loss Position, Fair Value	141,778,000		92,768,000		619,000
Investment Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Investment Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	581,000		483,000		7,000
Investment Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	0		0		0
Investment Securities, Continuous Unrealized Loss Position, Aggregate Losses	581,000		483,000		7,000
Other than Temporary Impairment Losses, Investment Securities, Portion Recognized in Earnings, Net, Qualitative Disclosures, Lowest Current Credit Rating [Abstract]
Investment Securities, Portfolio Concentration US Govt or GSE Securities Not Rated, Carrying Value	0	[5]
Investment Securities, Portfolio Concentration US Govt or GSE Securities Not Rated, Fair Value	0	[5]
Investment Securities, Portfolio Concentration Rated AAA to AA, Carrying Value	260,791,000
Investment Securities, Portfolio Concentration Rated AAA to AA, Fair Value	261,492,000
Investment Securities, Portfolio Concentration Rated A to BBB, Carrying Value	25,360,000
Investment Securities, Portfolio Concentration Rated A to BBB, Fair Value	25,887,000
Investment Securities, Portfolio Concentration Rated Below Investment Grade, Carrying Value	0
Investment Securities, Portfolio Concentration Rated Below Investment Grade, Fair Value	0
Investment Securities, Portfolio Concentration Not Rated, Carrying Value	52,852,000
Investment Securities, Portfolio Concentration Not Rated, Fair Value	54,561,000
Other Debt Securities [Member]
Schedule of Investment (Held-to-Maturity) Securities [Line Items]
Investment Securities, Amortized Cost	177,300,000		184,067,000		183,431,000
Investments Securities, Carrying Value	177,300,000	[1]	184,067,000	[2]	183,431,000	[3]
Investment Securities, Fair Value	196,403,000		206,575,000		202,171,000
Investment Securities, Gross Unrealized Gain	19,153,000	[4]	22,528,000	[4]	18,740,000	[4]
Investment Securities, Gross Unrealized Loss	(50,000)	[4]	(20,000)	[4]	0	[4]
Investment Securities, Debt Maturities, Net Carrying Value [Abstract]
Investment Securities, Debt Maturities, Less than One Year, Net Carrying Value	9,688,000
Investment Securities, Debt Maturities, One to Five Years, Net Carrying Value	31,978,000
Investment Securities, Debt Maturities, Six to Ten Years, Net Carrying Value	35,164,000
Investment Securities, Debt Maturities, Over Ten Years, Net Carrying Value	100,470,000
Investment Securities, Debt Maturities, Net Carrying Value	177,300,000
Investment Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Investment Securities, Debt Maturities, Less Than One Year, Fair Value	9,768,000
Investment Securities, Debt Maturities, One to Five Years, Fair Value	33,041,000
Investment Securities, Debt Maturities, Six to Ten Years, Fair Value	37,922,000
Investment Securities, Debt Maturities, Over Ten Years, Fair Value	115,672,000
Investment Securities, Debt Maturities, Fair Value	196,403,000
Investment Securities, Debt Maturities, Nominal Yield [Abstract]
Investment Securities, Debt Maturities, Less Than One Year, Nominal Yield	4.21%
Investment Securities, Debt Maturities, One to Five Years, Nominal Yield	5.16%
Investment Securities, Debt Maturities, Six to Ten Years, Nominal Yield	5.57%
Investment Securities, Debt Maturities, Over Ten Years, Nominal Yield	6.29%
Investment Securities, Debt Maturities, Nominal Yield	5.83%
Investment Securities, Debt Maturities, Weighted Average Maturity	9.26	[6]
Investment Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Investment Securities, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	14		14		0
Investment Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Investment Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	852,000		881,000		0
Investment Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0		0		0
Investment Securities, Continuous Unrealized Loss Position, Fair Value	852,000		881,000		0
Investment Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Investment Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	50,000		20,000		0
Investment Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	0		0		0
Investment Securities, Continuous Unrealized Loss Position, Aggregate Losses	50,000		20,000		0
Other than Temporary Impairment Losses, Investment Securities, Portion Recognized in Earnings, Net, Qualitative Disclosures, Lowest Current Credit Rating [Abstract]
Investment Securities, Portfolio Concentration US Govt or GSE Securities Not Rated, Carrying Value	0	[5]
Investment Securities, Portfolio Concentration US Govt or GSE Securities Not Rated, Fair Value	0	[5]
Investment Securities, Portfolio Concentration Rated AAA to AA, Carrying Value	167,463,000
Investment Securities, Portfolio Concentration Rated AAA to AA, Fair Value	186,460,000
Investment Securities, Portfolio Concentration Rated A to BBB, Carrying Value	600,000
Investment Securities, Portfolio Concentration Rated A to BBB, Fair Value	600,000
Investment Securities, Portfolio Concentration Rated Below Investment Grade, Carrying Value	0
Investment Securities, Portfolio Concentration Rated Below Investment Grade, Fair Value	0
Investment Securities, Portfolio Concentration Not Rated, Carrying Value	9,237,000
Investment Securities, Portfolio Concentration Not Rated, Fair Value	9,343,000
U.S. Agency Residential Mortgage-backed Securities [Member] | Other [Member]
Schedule of Investment (Held-to-Maturity) Securities [Line Items]
Investment Securities, Amortized Cost	69,075,000		77,726,000		103,055,000
Investments Securities, Carrying Value	72,968,000	[1]	82,767,000	[2]	112,909,000	[3]
Investment Securities, Fair Value	76,851,000		85,943,000		113,958,000
Investment Securities, Gross Unrealized Gain	3,883,000	[4]	3,176,000	[4]	1,587,000	[4]
Investment Securities, Gross Unrealized Loss	0	[4]	0	[4]	(538,000)	[4]
Investment Securities, Debt Maturities, Net Carrying Value [Abstract]
Investment Securities, Debt Maturities, Net Carrying Value	72,968,000
Investment Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Investment Securities, Debt Maturities, Fair Value	76,851,000
Investment Securities, Debt Maturities, Nominal Yield [Abstract]
Investment Securities, Debt Maturities, Nominal Yield	2.71%	[8]
Investment Securities, Debt Maturities, Average Expected Life of Mortgage-backed Securities	3.6
Investments Securities, Transfers [Abstract]
Investment Securities, Transferred From Available For Sale Securities Portfolio, Fair Value							131,000,000
Investment Securities, Transferred From Available For Sale Securities Portfolio, Amortized Cost							118,000,000
Investment Securities, Transferred From Available For Sale Securities Portfolio, Net Unrealized Gain	3,900,000		5,000,000		9,900,000		13,000,000
Investment Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Investment Securities, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	0		0		2
Investment Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Investment Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	0		0		45,668,000
Investment Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0		0		0
Investment Securities, Continuous Unrealized Loss Position, Fair Value	0		0		45,668,000
Investment Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Investment Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	0		0		538,000
Investment Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	0		0		0
Investment Securities, Continuous Unrealized Loss Position, Aggregate Losses	0		0		538,000
Other than Temporary Impairment Losses, Investment Securities, Portion Recognized in Earnings, Net, Qualitative Disclosures, Lowest Current Credit Rating [Abstract]
Investment Securities, Portfolio Concentration US Govt or GSE Securities Not Rated, Carrying Value	72,968,000	[5]
Investment Securities, Portfolio Concentration US Govt or GSE Securities Not Rated, Fair Value	76,851,000	[5]
Investment Securities, Portfolio Concentration Rated AAA to AA, Carrying Value	0
Investment Securities, Portfolio Concentration Rated AAA to AA, Fair Value	0
Investment Securities, Portfolio Concentration Rated A to BBB, Carrying Value	0
Investment Securities, Portfolio Concentration Rated A to BBB, Fair Value	0
Investment Securities, Portfolio Concentration Rated Below Investment Grade, Carrying Value	0
Investment Securities, Portfolio Concentration Rated Below Investment Grade, Fair Value	0
Investment Securities, Portfolio Concentration Not Rated, Carrying Value	0
Investment Securities, Portfolio Concentration Not Rated, Fair Value	$ 0

[1] Carrying value includes $3.9 million of net unrealized gain which remains in Accumulated other comprehensive income (“AOCI”) related to certain securities transferred from the Available for Sale securities portfolio to the Investment securities portfolio as discussed in greater detail following.

[2] Carrying value includes $5.0 million of net unrealized gain which remains in Accumulated other comprehensive income (“AOCI”) in the Consolidated Balance Sheets related to certain securities transferred from the Available for Sale securities portfolio to the Investment securities portfolio as discussed in greater detail following.

[3] Carrying value includes $9.9 million of net unrealized gain which remains in Accumulated other comprehensive income (“AOCI”) in the Consolidated Balance Sheets related to certain securities transferred from the Available for Sale securities portfolio to the Investment securities portfolio as discussed in greater detail following.

[4] Gross unrealized gains and losses are not recognized in AOCI in the Consolidated Balance Sheets.

[5] U.S. government and government sponsored enterprises are not rated by the nationally-recognized rating agencies as these securities are guaranteed by agencies of the U.S. government or government-sponsored enterprises.

[6] Expected maturities may differ from contractual maturities, because borrowers may have the right to call or prepay obligations with or without penalty.

[7] Calculated on a taxable equivalent basis using a 39% effective tax rate.

[8] The nominal yield on residential mortgage-backed securities is based upon prepayment assumptions at the purchase date. Actual yields earned may differ significantly based upon actual prepayments. See Quarterly Financial Summary - Unaudited for current yields on the investment securities portfolio.