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Summary of Significant Accounting Policies Cash and Cash Equivalents (Details) - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Cash and Cash Equivalents [Abstract]        
Cash and cash equivalents $ 203,104 $ 193,862 $ 158,821  
Restricted cash 24,175 16,488 19,030  
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents $ 227,279 $ 210,350 $ 177,851 $ 163,448