Fair Value Measurements (Details 2) (USD $)	Sep. 30, 2013	Dec. 31, 2012
Assets
Restricted cash	$ 47,466,000	$ 38,717,000
Liabilities
Contingent consideration	759,000
Fair value measured on a recurring basis | Quoted prices in active markets (Level 1)
Assets
Cash and cash equivalents	127,902,000	168,056,000
Restricted cash	47,466,000	38,717,000
Investments in lieu of retainage	10,808,000	10,553,000
Total assets	186,176,000	217,326,000
Fair value measured on a recurring basis | Significant other observable inputs (Level 2)
Assets
Short-term investments	2,151,000	2,679,000
Investments in lieu of retainage	8,903,000	11,381,000
Total assets	11,054,000	14,060,000
Liabilities
Interest rate swap contract	1,151,000	1,923,000
Total liabilities	1,151,000	1,923,000
Fair value measured on a recurring basis | Significant unobservable inputs (Level 3)
Assets
Long-term investments - auction rate securities	46,283,000	46,283,000
Total assets	46,283,000	46,283,000
Liabilities
Contingent consideration	57,872,000	42,624,000
Total liabilities	57,872,000	42,624,000
Total Carrying Value
Assets
Cash and cash equivalents	127,902,000	168,056,000
Restricted cash	47,466,000	38,717,000
Short-term investments	2,151,000	2,679,000
Investments in lieu of retainage	19,711,000	21,934,000
Long-term investments - auction rate securities	46,283,000	46,283,000
Total assets	243,513,000	277,669,000
Liabilities
Interest rate swap contract	1,151,000	1,923,000
Contingent consideration	57,872,000	42,624,000
Total liabilities	$ 59,023,000	$ 44,547,000