Fair Value Measurements (Details) (USD $)	6 Months Ended	3 Months Ended								6 Months Ended
	Jun. 30, 2012	Jun. 30, 2012 Contingent Consideration [Member]	Mar. 31, 2012 Contingent Consideration [Member]	Jun. 30, 2011 Contingent Consideration [Member]	Mar. 31, 2011 Contingent Consideration [Member]	Jun. 30, 2012 Auction Rate Securities [Member]	Mar. 31, 2012 Auction Rate Securities [Member]	Jun. 30, 2011 Auction Rate Securities [Member]	Mar. 31, 2011 Auction Rate Securities [Member]	Jun. 30, 2012 Term Loan [Member]	Jun. 30, 2012 Maximum [Member]	Jun. 30, 2012 Maximum [Member] Contingent Consideration [Member]	Jun. 30, 2012 Minimum [Member]	Jun. 30, 2012 Minimum [Member] Contingent Consideration [Member]	Jun. 30, 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]		Jun. 30, 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]		Jun. 30, 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]		Jun. 30, 2012 Carrying Amount [Member]		Dec. 31, 2011 Carrying Amount [Member]		Jun. 30, 2012 Fair Value [Member]
Assets [Abstract]
Cash and Cash Equivalents															$ 185,386,000	[1]	$ 204,240,000	[1]	$ 0	[1]	$ 0	[1]	$ 0	[1]	$ 0	[1]	$ 185,386,000	[1]	$ 204,240,000	[1]
Restricted Cash															38,684,000	[1]	35,437,000	[1]	0	[1]	0	[1]	0	[1]	0	[1]	38,684,000	[1]	35,437,000	[1]
Short term investments, Fair Value Disclosure															0	[2]	1,026,000	[2]	3,666,000	[2]	2,439,000	[2]	0	[2]	0	[2]	3,666,000	[2]	3,465,000	[2]
Bonds substituted for retainage															0	[3]	0	[3]	15,182,000	[3]	12,488,000	[3]	0	[3]	0	[3]	15,182,000	[3]	12,488,000	[3]
Long-term Investments, Auction rate securities, fair value disclosure															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															224,070,000		240,703,000		18,848,000		14,927,000		46,283,000		62,311,000		289,201,000		317,941,000
Liabilities [Abstract]
Interest rate swap contract															0	[5]	0	[5]	1,916,000	[5]	0	[5]	0	[5]	0	[5]	1,916,000	[5]	0	[5]
Contingent consideration															0	[6]	0	[6]	0	[6]	0	[6]	54,743,000	[6]	51,555,000	[6]	54,743,000	[6]	51,555,000	[6]
Total Liabilities															0		0		1,916,000		0		54,743,000		51,555,000		56,659,000		51,555,000
Fixed rate senior unsecured notes																											298,100,000				302,300,000
Assets [Abstract]
Cash and Cash Equivalents															185,386,000	[1]	204,240,000	[1]	0	[1]	0	[1]	0	[1]	0	[1]	185,386,000	[1]	204,240,000	[1]
Restricted Cash															38,684,000	[1]	35,437,000	[1]	0	[1]	0	[1]	0	[1]	0	[1]	38,684,000	[1]	35,437,000	[1]
Short term investments, Fair Value Disclosure															0	[2]	1,026,000	[2]	3,666,000	[2]	2,439,000	[2]	0	[2]	0	[2]	3,666,000	[2]	3,465,000	[2]
Bonds substituted for retainage															0	[3]	0	[3]	15,182,000	[3]	12,488,000	[3]	0	[3]	0	[3]	15,182,000	[3]	12,488,000	[3]
Long-term Investments, Auction rate securities, fair value disclosure															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															224,070,000		240,703,000		18,848,000		14,927,000		46,283,000		62,311,000		289,201,000		317,941,000
Liabilities [Abstract]
Interest rate swap contract															0	[5]	0	[5]	1,916,000	[5]	0	[5]	0	[5]	0	[5]	1,916,000	[5]	0	[5]
Contingent consideration															0	[6]	0	[6]	0	[6]	0	[6]	54,743,000	[6]	51,555,000	[6]	54,743,000	[6]	51,555,000	[6]
Total Liabilities															0		0		1,916,000		0		54,743,000		51,555,000		56,659,000		51,555,000
Fixed rate senior unsecured notes																											298,100,000				302,300,000
Maturity period for cash cash equivalents and restricted cash, maximum	3 months
Fair value inputs, discount rate											7.00%	18.00%	3.00%	14.00%
Term of auction rate securities (in years)											8 years		6 years
Debt Instrument [Line Items]
Long-term debt										200,000,000
Term of loan										5 years
Assets measured at fair value on a recurring basis using significant unobservable inputs [Roll Forward]
Beginning Balance						46,283,000	62,311,000	88,129,000	88,129,000
Purchases						0	0	0	0
Settlements						0	(16,553,000)	0	0
Realized loss on sale of investments							(2,699,000)
Reversal of pretax impairment charges included in accumulated other comprehensive income (loss)							3,224,000
Ending Balance						46,283,000	46,283,000	88,129,000	88,129,000
Estimated recovery period for auction rate securities						12 months
Liabilities measured at fair value on a recurring basis using significant unobservable inputs [Roll Forward]
Beginning balance		51,697,000	51,555,000	4,200,000	0
Fair value adjustments included in other income (expense), net		(298,000)	142,000
Fair value measured at conclusion of purchase price analysis measurement period		3,344,000
Fair value measured prior to the conclusion of purchase price analysis measurement period				5,500,000	4,200,000
Ending balance		$ 54,743,000	$ 51,697,000	$ 9,700,000	$ 4,200,000
Fair value inputs, discount rate											7.00%	18.00%	3.00%	14.00%

[1] Cash, cash equivalents and restricted cash consist primarily 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 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] Bonds substituted for retainage are classified as accounts receivable, including retainage and are comprised of U.S. Treasury Notes and other municipal bonds, the majority of which are rated Aa2 or better. The fair values of these assets are obtained from readily-available pricing sources for comparable instruments, and as such, the Company has classified these assets as Level 2.

[4] At June 30, 2012 the Company had $46.3 million 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 June 30, 2012 are in securities collateralized by student loan portfolios. At June 30, 2012 most of the Company’s ARS are rated AAA. The Company estimated the fair value of its ARS utilizing an income approach valuation model which considered, among other items, the following inputs: (i) prices from recent comparable transactions; (ii) other third-party pricing information without adjustment; (iii) the underlying structure of each security; (iv) the present value of future principal and interest payments discounted at rates considered to reflect current market conditions (discount rates range from 3-7%); and (v) consideration of the probabilities of default or repurchase at par for each period (term periods range from 6-8 years).

[5] As discussed in Note 10, 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 June 30, 2012 above represent the contingent consideration for the Company’s recent acquisitions for which the measurement period for purchase price analysis has concluded. See the level 3 rollforward below for disclosure of the Company’s valuation approach.