Fair Value Measurements, Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) (USD $)	12 Months Ended		12 Months Ended
	Dec. 31, 2012 Term Loan [Member]	Aug. 03, 2011 Term Loan [Member]	Dec. 31, 2012 Minimum [Member] Auction Rate Securities [Member] Income Approach Valuation Model [Member]	Dec. 31, 2012 Maximum [Member] Auction Rate Securities [Member] Income Approach Valuation Model [Member]	Dec. 31, 2012 Fair Value Measured on a Recurring Basis [Member] Quoted Prices in Active Markets (Level 1) [Member]		Dec. 31, 2011 Fair Value Measured on a Recurring Basis [Member] Quoted Prices in Active Markets (Level 1) [Member]		Dec. 31, 2012 Fair Value Measured on a Recurring Basis [Member] Significant Other Observable Inputs (Level 2) [Member]		Dec. 31, 2011 Fair Value Measured on a Recurring Basis [Member] Significant Other Observable Inputs (Level 2) [Member]		Dec. 31, 2012 Fair Value Measured on a Recurring Basis [Member] Significant Unobservable Inputs (Level 3) [Member]		Dec. 31, 2011 Fair Value Measured on a Recurring Basis [Member] Significant Unobservable Inputs (Level 3) [Member]		Dec. 31, 2012 Fair Value [Member]	Dec. 31, 2011 Fair Value [Member]	Dec. 31, 2012 Carrying Value [Member]		Dec. 31, 2011 Carrying Value [Member]
Long-term Debt [Abstract]
Fixed rate senior unsecured notes																	$ 309,800,000	$ 280,500,000	$ 298,300,000		$ 298,000,000
Other fixed rate debt																	145,400,000	167,700,000	140,700,000		162,300,000
Variable rate debt																	298,100,000	212,200,000	298,100,000		212,200,000
Assets [Abstract]
Cash and cash equivalents					168,056,000	[1]	204,240,000	[1]	0	[1]	0	[1]	0	[1]	0	[1]			168,056,000	[1]	204,240,000	[1]
Restricted cash					38,717,000	[1]	35,437,000	[1]	0	[1]	0	[1]	0	[1]	0	[1]			38,717,000	[1]	35,437,000	[1]
Short term investments					0	[2]	1,026,000	[2]	2,679,000	[2]	2,439,000	[2]	0	[2]	0	[2]			2,679,000	[2]	3,465,000	[2]
Investments in lieu of retainage					10,553,000	[3]	0	[3]	11,381,000	[3]	12,488,000	[3]	0	[3]	0	[3]			21,934,000	[3]	12,488,000	[3]
Long-term Investments - Auction rate securities					0	[4]	0	[4]	0	[4]	0	[4]	46,283,000	[4]	62,311,000	[4]			46,283,000	[4]	62,311,000	[4]
Total assets					217,326,000		240,703,000		14,060,000		14,927,000		46,283,000		62,311,000				277,669,000		317,941,000
Liabilities [Abstract]
Interest rate swap contract					0	[5]	0	[5]	1,923,000	[5]	0	[5]	0	[5]	0	[5]			1,923,000	[5]	0	[5]
Contingent consideration					0	[6]	0	[6]	0	[6]	0	[6]	42,624,000	[6]	51,555,000	[6]			42,624,000	[6]	51,555,000	[6]
Total liabilities					0		0		1,923,000		0		42,624,000		51,555,000				44,547,000		51,555,000
Fair Value Inputs [Abstract]
Fair value inputs, discount rate (in hundredths)			3.00%	7.00%
Fair value inputs, term of auction rate securities (in years)			6 years	8 years
Long-term Debt [Abstract]
Face amount	$ 200,000,000	$ 200,000,000
Term of loan	5 years

[1] Cash, cash equivalents and restricted cash primarily consist of money market funds with original maturity dates of three months or less, for which fair value is determined through quoted market prices.

[2] Short-term investments are classified as other current assets and are comprised of municipal bonds. The majority of the municipal bonds are rated Aa2 or better. The fair values of the municipal bonds are obtained from readily-available pricing sources for comparable instruments, and as such, the Company has classified these assets as Level 2.

[3] Investments in lieu of retainage are classified as accounts receivable, including retainage and are comprised of money market funds, U.S. Treasury Notes and other municipal bonds, the majority of which are rated Aa3 or better. The fair values of the U.S. Treasury Notes and municipal bonds are obtained from readily-available pricing sources for comparable instruments, and as such, the Company has classified these assets as Level 2.

[4] At December 31, 2012 and 2011 the Company had $46.3 million and $62.3 million, respectively, invested in auction rate securities (“ARS”) which the Company considers as available-for-sale long-term investments. The long-term investments ARS held by the Company at December 31, 2012 and 2011 are in securities collateralized by student loan portfolios. At December 31, 2012 and 2011, most of the Company’s ARS were rated AA+ and AAA, respectively. The Company estimated the fair value of its ARS utilizing an income approach valuation model which considered, among other items, the following inputs: (i) the underlying structure of each security; (ii) the present value of future principal and interest payments discounted at rates considered to reflect current market conditions (discount rates range from 3% to 7%); (iii) consideration of the probabilities of default or repurchase at par for each period (term periods range from 6 to 8 years); (iv) prices from recent comparable transactions; and (v) other third party pricing information without adjustment.

[5] As discussed in Note 5 – Financial Commitments, the Company entered into a swap agreement with Bank of America, N.A. to establish a long-term interest rate for its $200 million five-year term loan. The swap agreement became effective for the term loan principal balance outstanding at January 31, 2012 and will remain effective through the maturity date of the term loan. The Company values the interest rate swap liability utilizing a discounted cash flow model that takes into consideration forward interest rates observable in the market and the counterparty’s credit risk. This liability is classified as a component of other long-term liabilities.

[6] The liabilities listed as of December 31, 2012 and 2011 above represent the contingent consideration for the Company’s acquisitions in 2011 for which the measurement period for purchase price analysis has concluded.