Summary of Significant Accounting Policies (Schedule of Cash and Cash Equivalents) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Total cash and cash equivalents	$ 192,868	$ 146,103	$ 75,452	$ 135,583
Consolidated Entity, Excluding Joint Venture [Member]
Total cash and cash equivalents	94,713	49,539
Joint Venture [Member]
Total cash and cash equivalents	$ 98,155	$ 96,564