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Retirement Savings Plan (Narrative) (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Defined Contribution Pension and Other Postretirement Plans Disclosure [Abstract]      
Expense related to contribution to employees' retirement accounts $ 8,665 $ 13,669 $ 11,460