Fair Value Measurements (Schedule of Financial Statement Items Carried at Estimated Fair Value)(Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Jun. 05, 2014	Aug. 03, 2011
Assets:
Restricted cash	$ 44,370,000	$ 42,594,000
Fair Value Measured On A Recurring Basis [Member] | Quoted Prices In Active Markets (Level 1) [Member]
Assets:
Cash and cash equivalents	135,583,000	119,923,000
Restricted cash	44,370,000	42,594,000
Investments in lieu of retainage	25,761,000	12,184,000
Total assets	205,714,000	174,701,000
Fair Value Measured On A Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets:
Short-term investments		2,336,000
Investments in lieu of retainage	7,463,000	9,729,000
Total assets	7,463,000	12,065,000
Liabilities:
Interest rate swap contract	381,000	974,000
Total liabilities	381,000	974,000
Fair Value Measured On A Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets:
Long-term investments - auction rate securities		46,283,000
Total assets		46,283,000
Liabilities:
Contingent consideration	24,814,000	46,022,000
Total liabilities	24,814,000	46,022,000
Carrying Value [Member]
Assets:
Cash and cash equivalents	135,583,000	119,923,000
Restricted cash	44,370,000	42,594,000
Short-term investments		2,336,000
Investments in lieu of retainage	33,224,000	21,913,000
Long-term investments - auction rate securities		46,283,000
Total assets	213,177,000	233,049,000
Liabilities:
Interest rate swap contract	381,000	974,000
Contingent consideration	24,814,000	46,022,000
Total liabilities	25,195,000	46,996,000
Minimum [Member]
Liabilities:
Fair value inputs, discount rate (in hundredths)	14.00%
Maximum [Member]
Liabilities:
Fair value inputs, discount rate (in hundredths)	18.00%
Income Approach Valuation Model [Member] | Minimum [Member] | ARS [Member]
Liabilities:
Fair value inputs, discount rate (in hundredths)	3.00%
Fair value inputs, term of auction rate securities	6 years
Income Approach Valuation Model [Member] | Maximum [Member] | ARS [Member]
Liabilities:
Fair value inputs, discount rate (in hundredths)	7.00%
Fair value inputs, term of auction rate securities	8 years
Term Loan [Member]
Liabilities:
Face amount	250,000,000	200,000,000	250,000,000	200,000,000
Period of term loan	5 years	5 years
Term Loan [Member] | Maximum [Member]
Liabilities:
Face amount			$ 300,000,000