Fair Value Measurements (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Assets:
Restricted cash	$ 48,725	$ 45,853
Fair Value Measured On A Recurring Basis [Member] | Quoted Prices In Active Markets (Level 1) [Member]
Assets:
Cash and cash equivalents	170,744	75,452
Restricted cash	48,725	45,853
Investments in lieu of retainage	43,820	35,350
Total assets	263,289	156,655
Fair Value Measured On A Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets:
Investments in lieu of retainage	4,605	6,216
Total assets	4,605	6,216
Liabilities:
Interest rate swap contract		45
Total liabilities		45
Carrying Value [Member] | Fair Value Measured On A Recurring Basis [Member]
Assets:
Cash and cash equivalents	170,744	75,452
Restricted cash	48,725	45,853
Investments in lieu of retainage	48,425	41,566
Total assets	$ 267,894	162,871
Liabilities:
Interest rate swap contract		45
Total liabilities		$ 45