Short-Term Borrowings (Details) (USD $)	12 Months Ended				12 Months Ended						3 Months Ended
	Dec. 31, 2012 Maximum [Member] Credit Agreement [Member]	Dec. 31, 2012 Bank of America, N.A. [Member] Credit Agreement [Member] entity	Nov. 30, 2012 Bank of America, N.A. [Member] Credit Agreement [Member]	Dec. 31, 2012 Revolving Credit Facility [Member] Credit Agreement [Member]	Dec. 31, 2012 Revolving Credit Facility [Member] Bank of America, N.A. [Member] Minimum [Member] Credit Agreement [Member]	Dec. 31, 2012 Revolving Credit Facility [Member] Bank of America, N.A. [Member] Maximum [Member] Credit Agreement [Member]	Dec. 31, 2012 Revolving Credit Facility [Member] Bank of America, N.A. [Member] Applicable Rate [Member] Minimum [Member] Credit Agreement [Member]	Dec. 31, 2012 Revolving Credit Facility [Member] Bank of America, N.A. [Member] Applicable Rate [Member] Maximum [Member] Credit Agreement [Member]	Dec. 31, 2012 Revolving Credit Facility [Member] Bank of America, N.A. [Member] Base Rate [Member] Minimum [Member] Credit Agreement [Member]	Dec. 31, 2012 Revolving Credit Facility [Member] Bank of America, N.A. [Member] Base Rate [Member] Maximum [Member] Credit Agreement [Member]	Dec. 31, 2012 Revolving Credit Facility [Member] JPMorgan Chase Bank, N.A. [Member]	Dec. 31, 2011 Revolving Credit Facility [Member] JPMorgan Chase Bank, N.A. [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity			$ 75,000,000
Line of Credit Facility, Overdraft Facility			5,000,000
Number of Indirect Subsidiaries Guaranteeing Line of Credit Facility		3
Debt Instrument, Basis Spread on Variable Rate							1.25%	2.00%	0.25%	1.00%
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage					0.15%	0.225%
Ratio of Consolidated Fund Indebtedness to Earning Before Interest Taxes Depreciation Amortization	2.5
Fixed Charge Coverage Ratio	1.2
Number of Borrowers, Line of Credit Facility		3
Remaining borrowing capacity under line of credit				69,100,000
Debt Instrument, Interest Rate, Effective Percentage				1.46%
Fees paid to fully collateralize letter of credit											400,000
Amount outstanding on line of credit				2,800,000								0
Letters of Credit Outstanding, Amount				$ 3,100,000