Retirement Plans - Amounts Expected to be Recognized as Components of Net Periodic Pension Costs (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($)
Pension plan
Amounts expected to be recognized as component of net periodic pension costs during the next fiscal year:
Amortization net actuarial gain or (loss)	$ 230
Amortization prior service cost	(29)
SERP
Amounts expected to be recognized as component of net periodic pension costs during the next fiscal year:
Amortization net actuarial gain or (loss)	$ 372