Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Components of accumulated other comprehensive loss	$ 180,884	$ 173,793	$ 168,137	$ 160,307	$ 156,605	$ 153,966
Unrealized Gains (Losses) on Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Components of accumulated other comprehensive loss	946		(1,651)	(2,748)
Pension Liability
Accumulated Other Comprehensive Income (Loss) [Line Items]
Components of accumulated other comprehensive loss	(7,238)		(7,566)	(5,935)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Components of accumulated other comprehensive loss	$ (6,292)	$ (7,943)	$ (9,217)	$ (8,683)	$ (8,281)	$ (7,092)