Other Comprehensive Income/Loss - Components of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at the beginning of the period	$ (65,951)	$ (38,250)
Other Comprehensive Income (Loss)	7,334	(27,701)	$ 34,840
Balance at the end of the period	(58,617)	(65,951)	(38,250)
Net unrealized gain (loss) on securities available-for-sale
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at the beginning of the period	4,686	(4,366)
Other Comprehensive Income (Loss)	(1,859)	9,052
Balance at the end of the period	2,827	4,686	(4,366)
Net actuarial loss on pension plans and other postretirement benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at the beginning of the period	(67,476)	(30,600)
Other Comprehensive Income (Loss)	9,080	(36,876)
Balance at the end of the period	(58,396)	(67,476)	(30,600)
Prior service cost on pension plans and other postretirement benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at the beginning of the period	(3,161)	(3,284)
Other Comprehensive Income (Loss)	113	123
Balance at the end of the period	$ (3,048)	$ (3,161)	$ (3,284)