Supplemental Disclosures of Cash Flow Information and Non-Cash Financing and Investing Activities Restricted Cash (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash and Cash Equivalents, at Carrying Value	$ 573,383,000	$ 515,646,000	$ 443,420,000
Restricted Cash and Cash Equivalents	250,705,000	265,637,000	229,753,000
Cash and Cash Equivalents inclusive of Restricted Cash [Member]
Cash and Cash Equivalents, at Carrying Value	$ 824,088,000	$ 781,283,000	$ 673,173,000