Employee Benefit Plans - Summary of amounts recognized in consolidated balance sheets (Details 1) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Long-term pension liabilities	$ (32,864)	$ (33,009)
Retirement Income Plan
Defined Benefit Plan Disclosure [Line Items]
Funded status of the Retirement Income Plan	(9,570)	(11,957)
SERP liability	(23,294)	(21,052)
Long-term pension liabilities	$ (32,864)	$ (33,009)