Stockholders' Equity (Details 2) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
AOCI Attributable to Parent, Net of Tax
Balance at the beginning of the period			$ 786,084
Net current period other comprehensive income (loss)			(1,721)
Balance at the end of the period	$ 836,937		836,937
Accumulated Other Comprehensive Income(Loss)
AOCI Attributable to Parent, Net of Tax
Balance at the beginning of the period	(51,731)	$ (13,756)	(50,443)	$ (15,859)
Other comprehensive income (loss) before reclassification	(3,427)	(3,674)	(3,807)	377
Amount reclassified from accumulated other comprehensive income	2,994	(973)	2,086	(2,921)
Net current period other comprehensive income (loss)	(433)	(4,647)	(1,721)	(2,544)
Balance at the end of the period	(52,164)	(18,403)	(52,164)	(18,403)
Unrealized (gains) losses on investment securities
AOCI Attributable to Parent, Net of Tax
Balance at the beginning of the period	(2,713)	4,078	(727)	3,150
Other comprehensive income (loss) before reclassification	(2,165)	(2,317)	(2,387)	239
Amount reclassified from accumulated other comprehensive income	1,330	(813)	(434)	(2,441)
Net current period other comprehensive income (loss)	(835)	(3,130)	(2,821)	(2,202)
Balance at the end of the period	(3,548)	948	(3,548)	948
Change in valuation allowance for unrealized gains (losses) on investment securities
AOCI Attributable to Parent, Net of Tax
Balance at the beginning of the period	(2,649)	1,353	(1,471)	810
Other comprehensive income (loss) before reclassification	(1,262)	(1,357)	(1,420)	138
Amount reclassified from accumulated other comprehensive income	776	(475)	(244)	(1,427)
Net current period other comprehensive income (loss)	(486)	(1,832)	(1,664)	(1,289)
Balance at the end of the period	(3,135)	(479)	(3,135)	(479)
Pension and postretirement benefits
AOCI Attributable to Parent, Net of Tax
Balance at the beginning of the period	(46,369)	(19,187)	(48,245)	(19,819)
Amount reclassified from accumulated other comprehensive income	888	315	2,764	947
Net current period other comprehensive income (loss)	888	315	2,764	947
Balance at the end of the period	$ (45,481)	$ (18,872)	$ (45,481)	$ (18,872)