Fair Value Measurements Fair Value Measurements, Financial Instruments Measured On a Recurring Basis, Quantitative Information (Details) (Fair Value, Inputs, Level 3 [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended				12 Months Ended
	Mar. 31, 2013		Mar. 31, 2012		Dec. 31, 2012
Municipal and Other Tax-exempt Securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Asset, Par Value	$ 45,470		$ 46,100		$ 45,570
Fair Value Inputs, Asset, Amortized Cost	40,758	[1]	42,393	[1]	40,857	[1]
Fair Value Inputs, Asset, Fair Value	39,007		41,977		40,702
Municipal and Other Tax-exempt Securities [Member] | External Credit Rating, Investment Grade [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Asset, Par Value	28,470		29,100		28,570
Fair Value Inputs, Asset, Amortized Cost	28,374	[1]	28,997	[1]	28,473	[1]
Fair Value Inputs, Asset, Fair Value	27,120		28,853		28,318
Fair Value Measurements, Valuation Techniques	Discounted cash flows	[2]	Discounted cash flows	[3]	Discounted cash flows	[2]
Fair Value Measurements, Significant Unobservable Input	Interest rate spread		Interest rate spread		Interest rate spread
Fair Value Inputs, Assets, Discount Rate, Minimum	5.00%	[4]	1.00%	[5]	1.00%	[5]
Fair Value Inputs, Assets, Discount Rate, Maximum	5.50%	[4]	1.50%	[5]	1.50%	[5]
Fair Value Inputs, Assets, Discount Rate, Weighted Average	5.25%	[4]	1.25%	[5]	1.25%	[5]
Fair Value Inputs, Assets, Fair Value As Percentage of Par Value, Minimum	95.01%	[6]	98.88%	[6]	98.83%	[6]
Fair Value Inputs, Assets, Fair Value As Percentage of Par Value, Maximum	95.59%	[6]	99.49%	[6]	99.43%	[6]
Fair Value Inputs, Fair Value As Percentage of Par Value, Weighted Average	95.26%	[6]	99.14%	[6]	99.12%	[6]
Investment Grade Tax Exempt Securities Yield Spread Over Comparable Securities Minimum	458		75		75
Investment Grade Tax Exempt Securities Yield Spread Over Comparable Securities Maximum	519		80		80
Additional Decrease in Fair Value From a 100 Basis Point Increase in Interest Rate Spread	(262)
Municipal and Other Tax-exempt Securities [Member] | External Credit Rating, Non Investment Grade [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Asset, Par Value	17,000		17,000		17,000
Fair Value Inputs, Asset, Amortized Cost	12,384	[1]	13,396	[1]	12,384	[1]
Fair Value Inputs, Asset, Fair Value	11,887		13,124		12,384
Fair Value Measurements, Valuation Techniques	Discounted cash flows	[2]	Discounted cash flows	[3]	Discounted cash flows	[2]
Fair Value Measurements, Significant Unobservable Input	Interest rate spread		Interest rate spread		Interest rate spread
Fair Value Inputs, Assets, Discount Rate, Minimum	8.80%	[7]	6.18%	[8]	7.21%	[7]
Fair Value Inputs, Assets, Discount Rate, Maximum	11.20%	[7]	9.37%	[8]	9.83%	[7]
Fair Value Inputs, Assets, Discount Rate, Weighted Average	9.54%	[7]	6.95%	[8]	7.82%	[7]
Fair Value Inputs, Assets, Fair Value As Percentage of Par Value, Minimum	69.86%	[6]	74.96%	[9]	72.79%	[6]
Fair Value Inputs, Assets, Fair Value As Percentage of Par Value, Maximum	70.04%	[6]	75.19%	[9]	73.00%	[6]
Fair Value Inputs, Fair Value As Percentage of Par Value, Weighted Average	69.92%	[6]	75.03%	[9]	72.85%	[6]
Below Investment Grade Tax Exempt Securities Yield Spread Over Comparable Securities	700		600		700
Additional Decrease in Fair Value From a 100 Basis Point Increase in Interest Rate Spread	(343)
Other Debt Securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Asset, Par Value	5,400		5,900		5,400
Fair Value Inputs, Asset, Amortized Cost	5,400	[1]	5,900	[1]	5,400	[1]
Fair Value Inputs, Asset, Fair Value	5,193		5,900		5,399
Fair Value Measurements, Valuation Techniques	Discounted cash flows	[2]	Discounted cash flows	[3]	Discounted cash flows	[2]
Fair Value Measurements, Significant Unobservable Input	Interest rate spread		Interest rate spread		Interest rate spread
Fair Value Inputs, Assets, Discount Rate, Minimum	5.44%	[10]	1.47%	[10]	1.65%	[10]
Fair Value Inputs, Assets, Discount Rate, Maximum	5.71%	[10]	1.74%	[10]	1.71%	[10]
Fair Value Inputs, Assets, Discount Rate, Weighted Average	5.68%	[10]	1.72%	[10]	1.70%	[10]
Fair Value Inputs, Assets, Fair Value As Percentage of Par Value, Minimum	96.16%	[6]	98.88%	[6]	100.00%	[6]
Fair Value Inputs, Assets, Fair Value As Percentage of Par Value, Maximum	96.16%	[6]	99.49%	[6]	100.00%	[6]
Fair Value Inputs, Fair Value As Percentage of Par Value, Weighted Average	96.16%	[6]	99.14%	[6]	100.00%	[6]
Average Yields On Comparable Short-term Taxable Securities Maximum	1.00%		1.00%		1.00%
Additional Decrease in Fair Value From a 100 Basis Point Increase in Interest Rate Spread	(50)
Equity Securities and Mutual Funds [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Asset, Amortized Cost	2,420	[1]			2,161	[1]
Fair Value Inputs, Asset, Fair Value	2,472				2,161
Fair Value Measurements, Valuation Techniques	Tangible book value per share of publicly traded financial institutions of similar size, less liquidity discount.	[11],[2]			Tangible book value per share of publicly traded financial institutions of similar size, less liquidity discount.	[2]
Fair Value Measurements, Significant Unobservable Input	Peer group tangible book per share and liquidity discount.				Peer group tangible book per share and liquidity discount.
Fair Value Inputs, Assets, Liquidity Discount	20.00%				20.00%
Other assets - private equity funds [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Asset, Fair Value	$ 29,216		$ 30,993		$ 28,169
Fair Value Measurements, Valuation Techniques	Net asset value reported by underlying fund		Net asset value reported by underlying fund		Net asset value reported by underlying fund
Fair Value Measurements, Significant Unobservable Input	Net asset value reported by underlying fund		Net asset value reported by underlying fund		Net asset value reported by underlying fund

[1] Amortized cost reduced by other-than-temporary impairments recorded in earnings. See Note 2 for additional discussion.

[2] Discounted cash flows developed using discount rates primarily based on reference to interest rate spreads for comparable securities of similar duration and credit rating as determined by the nationally-recognized rating agencies, adjusted for lack of trading volume

[3] 1 Discounted cash flows developed using discount rates primarily based on reference to interest rate spreads for comparable securities of similar duration and credit rating as determined by the nationally-recognized rating agencies, adjusted for lack of trading volume

[4] Interest rate yields used to value investment grade tax-exempt securities represent a spread of 458 to 519 basis points over average yields for comparable tax-exempt securities.

[5] Interest rate yields used to value investment grade tax-exempt securities represent a spread of 75 to 80 basis points over average yields for comparable tax-exempt securities.

[6] Represents fair value as a percentage of par value

[7] Interest rate yields determined using a spread of 700 basis points over comparable municipal securities of varying durations.

[8] Interest rate yields determined using a spread of 600 basis points over comparable municipal securities of varying durations.

[9] Represents exchange-traded energy derivative contracts

[10] Interest rate yields used to value investment grade taxable securities based on comparable short-term taxable securities which are generally yielding less than 1%.

[11] Fair value of shares of a smaller privately-held financial institution were valued using the tangible book value per share of similarly sized financial institutions within the immediate geographical market with a discount of 20% due to the liquidity of the shares.