Significant Accounting Policies - Cash, Cash Equivalents and Restricted Cash (Details) - USD ($)	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Cash and cash equivalents	$ 199,796,000	$ 73,475,000
Restricted cash	19,865,000	20,950,000
Cash, Cash Equivalents And Restricted Cash	$ 219,661,000	$ 94,425,000	$ 84,336,000	$ 69,959,000