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Employee Retirement Plans (Details) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2015
Sep. 30, 2014
Sep. 30, 2015
Sep. 30, 2014
Defined Benefit Plan Disclosure [Line Items]        
Benefits earned during the period $ 411 $ 316 $ 1,232 $ 947
Interest cost on projected benefit obligation 674 647 2,021 1,939
Expected return on plan assets (593) (586) (1,777) (1,757)
Net amortization and deferral 445 176 1,335 530
Net pension expense $ 937 $ 553 $ 2,811 $ 1,659