Fair Value Measurements (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Assets:
Restricted cash	$ 60,158	$ 50,504
Fair Value Measured On A Recurring Basis [Member]
Assets:
Cash and cash equivalents	104,817	146,103
Restricted cash	60,158	50,504
Investments in lieu of retainage	53,852	51,266
Total assets	218,827	247,873
Fair Value Measured On A Recurring Basis [Member] | Quoted Prices In Active Markets (Level 1) [Member]
Assets:
Cash and cash equivalents	104,817	146,103
Restricted cash	60,158	50,504
Investments in lieu of retainage	50,317	46,855
Total assets	215,292	243,462
Fair Value Measured On A Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets:
Investments in lieu of retainage	3,535	4,411
Total assets	$ 3,535	$ 4,411