Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Components of accumulated other comprehensive loss	$ 153,256	$ 120,061	$ 120,754	$ 114,715
Unrealized Gains (Losses) on Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Components of accumulated other comprehensive loss	40	(266)	1,679
Pension Liability
Accumulated Other Comprehensive Income (Loss) [Line Items]
Components of accumulated other comprehensive loss	(5,429)	(5,758)	(5,552)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Components of accumulated other comprehensive loss	$ (5,389)	$ (6,024)	$ (3,873)	$ (4,726)