Fair Value Measurements (Details 2) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Assets:
Restricted cash	$ 42,594	$ 38,717
Fair value measured on a recurring basis | Quoted prices in active markets (Level 1)
Assets:
Cash and cash equivalents	119,923	168,056
Restricted cash	42,594	38,717
Investments in lieu of retainage	12,184	10,553
Total assets	174,701	217,326
Fair value measured on a recurring basis | Significant other observable inputs (Level 2)
Assets:
Short-term investments	2,336	2,679
Investments in lieu of retainage	9,729	11,381
Total assets	12,065	14,060
Liabilities:
Interest rate swap contract	974	1,923
Total liabilities	974	1,923
Fair value measured on a recurring basis | Significant unobservable inputs (Level 3)
Assets:
Long-term investments - auction rate securities	46,283	46,283
Total assets	46,283	46,283
Liabilities:
Contingent consideration	46,022	42,624
Total liabilities	46,022	42,624
Total Carrying Value
Assets:
Cash and cash equivalents	119,923	168,056
Restricted cash	42,594	38,717
Short-term investments	2,336	2,679
Investments in lieu of retainage	21,913	21,934
Long-term investments - auction rate securities	46,283	46,283
Total assets	233,049	277,669
Liabilities:
Interest rate swap contract	974	1,923
Contingent consideration	46,022	42,624
Total liabilities	$ 46,996	$ 44,547