Fair Value Measurements (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Assets:
Restricted cash	$ 49,158	$ 45,853
Fair Value Measured On A Recurring Basis [Member] | Quoted Prices In Active Markets (Level 1) [Member]
Assets:
Cash and cash equivalents	90,582	75,452
Restricted cash	49,158	45,853
Investments in lieu of retainage	37,988	35,350
Total assets	177,728	156,655
Fair Value Measured On A Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets:
Investments in lieu of retainage	6,048	6,216
Total assets	6,048	6,216
Liabilities:
Interest rate swap contract	17	45
Total liabilities	17	45
Carrying Value [Member] | Fair Value Measured On A Recurring Basis [Member]
Assets:
Cash and cash equivalents	90,582	75,452
Restricted cash	49,158	45,853
Investments in lieu of retainage	44,036	41,566
Total assets	183,776	162,871
Liabilities:
Interest rate swap contract	17	45
Total liabilities	$ 17	$ 45