Fair Value Measurements (Schedule of Financial Statement Items Carried at Estimated Fair Value)(Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended		0 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Apr. 30, 2014 ARS [Member]	Mar. 31, 2014 ARS [Member]	Dec. 31, 2013 ARS [Member]	Sep. 30, 2014 Fair value measured on a recurring basis [Member] Quoted prices in active markets (Level 1) [Member]		Dec. 31, 2013 Fair value measured on a recurring basis [Member] Quoted prices in active markets (Level 1) [Member]		Sep. 30, 2014 Fair value measured on a recurring basis [Member] Significant other observable inputs (Level 2) [Member]		Dec. 31, 2013 Fair value measured on a recurring basis [Member] Significant other observable inputs (Level 2) [Member]		Sep. 30, 2014 Fair value measured on a recurring basis [Member] Significant unobservable inputs (Level 3) [Member]		Dec. 31, 2013 Fair value measured on a recurring basis [Member] Significant unobservable inputs (Level 3) [Member]		Sep. 30, 2014 Carrying value [Member] Fair value measured on a recurring basis [Member]		Dec. 31, 2013 Carrying value [Member] Fair value measured on a recurring basis [Member]
Assets:
Cash and cash equivalents						$ 137,228	[1]	$ 119,923	[1]									$ 137,228	[1]	$ 119,923	[1]
Restricted cash	46,988	42,594				46,988	[1]	42,594	[1]									46,988	[1]	42,594	[1]
Short-term investments										2,545	[2]	2,336	[2]					2,545	[2]	2,336	[2]
Investments in lieu of retainage						21,599	[3]	12,184	[3]	8,212	[3]	9,729	[3]					29,811	[3]	21,913	[3]
Long-term investments - auction rate securities				46,300	46,300											46,283	[4]			46,283	[4]
Total assets						205,815		174,701		10,757		12,065				46,283		216,572		233,049
Liabilities:
Interest rate swap contract										502	[5]	974	[5]					502	[5]	974	[5]
Contingent consideration														25,184	[6]	46,022	[6]	25,184	[6]	46,022	[6]
Total liabilities										502		974		25,184		46,022		25,686		46,996
Proceeds from sale of securities	$ 44,497		$ 44,500

[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 primarily of municipal bonds, the majority of which 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 account receivables, including retainage and are comprised of 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] On April 30, 2014, the Company sold its auction rate securities (“ARS”) for $44.5 million. At both March 31, 2014 and December 31, 2013 the Company had $46.3 million invested in these ARS which the Company considered as available-for-sale long-term investments. The long-term investments in ARS held by the Company at both March 31, 2014 and December 31, 2013 were in securities collateralized by student loan portfolios. At both March 31, 2014 and December 31, 2013, most of the Company’s ARS were rated AA+.

[5] As discussed in Note 10 — Financial Commitments, the Company entered into a swap agreement with Bank of America, N.A. to establish a long-term interest rate for its former $200 million five-year term loan. The swap agreement became effective for the term loan principal balance outstanding at January 31, 2012. This term loan was paid off and the then current amount refinanced on June 5, 2014, providing for a $250 million term loan maturing on June 5, 2019. The interest rate swap continues on its original basis for the initial term and amount and finalizes on June 30, 2016. 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 September 30, 2014 and December 31, 2013 above represent the contingent consideration for the Company’s acquisitions in 2011 for which the measurement periods for purchase price analyses for the acquisitions have concluded.