Employee Benefit Plans - Summary of reconciliation of Level 3 assets held during year (Details 8) - Retirement Income Plan - Level 3 - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance	$ 4,345	$ 2,705
Net Realized and Unrealized Gains/(Losses)	349	154
Net Purchases, Issuances and Settlements	$ (1,025)	$ 1,486
Net Transfers In to (Out of) Level 3
Balance	$ 3,669	$ 4,345
Real Estate
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance	3,420	2,705
Net Realized and Unrealized Gains/(Losses)	279	133
Net Purchases, Issuances and Settlements	$ (1,475)	$ 582
Net Transfers In to (Out of) Level 3
Balance	$ 2,224	$ 3,420
Alternative/Opportunistic/Special funds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance	925
Net Realized and Unrealized Gains/(Losses)	70	$ 21
Net Purchases, Issuances and Settlements	$ 450	$ 904
Net Transfers In to (Out of) Level 3
Balance	$ 1,445	$ 925