Employee Benefit Plans - Summary of reconciliation of Level 3 assets held during year (Details 8) (Retirement Income Plan, Level 3, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance	$ 2,705
Net Realized and Unrealized Gains/(Losses)	154
Net Purchases, Issuances and Settlements	1,486
Net Transfers In to (Out of) Level 3
Balance	4,345
Real Estate
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance	2,705	2,730
Net Realized and Unrealized Gains/(Losses)	133	217
Net Purchases, Issuances and Settlements	582	(242)
Net Transfers In to (Out of) Level 3
Balance	3,420	2,705
Alternative/Opportunistic/Special funds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance
Net Realized and Unrealized Gains/(Losses)	21
Net Purchases, Issuances and Settlements	904
Net Transfers In to (Out of) Level 3
Balance	$ 925