Organization, Basis of Presentation and Recent Accounting Pronouncements (Recent Accounting Pronouncements) (Details 1) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
New Accounting Pronouncement, Early Adoption [Line Items]
Net Cash Provided by Operating Activities	$ 220,857	$ 151,455
Net Decrease in Cash and Cash Equivalents and Restricted Cash	(254,404)	(153,758)
Cash and Cash Equivalents and Restricted Cash	$ 416,412	621,194	$ 670,816	$ 774,952
As previously reported [Member]
New Accounting Pronouncement, Early Adoption [Line Items]
Increase in Restricted Cash		(7,266)
Net Cash Provided by Operating Activities		144,189
Net Decrease in Cash and Cash Equivalents and Restricted Cash		(161,024)
Cash and Cash Equivalents and Restricted Cash		593,183		754,207
Adjustment [Member]
New Accounting Pronouncement, Early Adoption [Line Items]
Increase in Restricted Cash		7,266
Net Cash Provided by Operating Activities		7,266
Net Decrease in Cash and Cash Equivalents and Restricted Cash		7,266
Cash and Cash Equivalents and Restricted Cash		28,011		20,745
As Adopted [Member]
New Accounting Pronouncement, Early Adoption [Line Items]
Increase in Restricted Cash		0
Net Cash Provided by Operating Activities		151,455
Net Decrease in Cash and Cash Equivalents and Restricted Cash		(153,758)
Cash and Cash Equivalents and Restricted Cash		$ 621,194		$ 774,952