Stockholders' Equity (Details 2) - - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
AOCI Attributable to Parent, Net of Tax
Balance at the beginning of the period	$ 786,084	$ 687,342	$ 510,240
Net current period other comprehensive loss	(11,062)	(34,584)	30,938
Balance at the end of the period	846,455	786,084	687,342
Accumulated Other Comprehensive Income(Loss)
AOCI Attributable to Parent, Net of Tax
Balance at the beginning of the period	(50,443)	(15,859)	(46,797)
Other comprehensive loss before reclassification	(13,824)	(30,706)
Amount reclassified from accumulated other comprehensive income	2,762	(3,878)
Net current period other comprehensive loss	(11,062)	(34,584)	30,938
Balance at the end of the period	(61,505)	(50,443)	(15,859)
Unrealized (gains) losses on investment securities
AOCI Attributable to Parent, Net of Tax
Balance at the beginning of the period	(727)	3,150
Other comprehensive loss before reclassification	(2,464)	(636)
Amount reclassified from accumulated other comprehensive income	(538)	(3,241)
Net current period other comprehensive loss	(3,002)	(3,877)
Balance at the end of the period	(3,729)	(727)	3,150
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	(1,471)	810
Other comprehensive loss before reclassification	(1,463)	(381)
Amount reclassified from accumulated other comprehensive income	(306)	(1,900)
Net current period other comprehensive loss	(1,769)	(2,281)
Balance at the end of the period	(3,240)	(1,471)	810
Pension and postretirement benefits
AOCI Attributable to Parent, Net of Tax
Balance at the beginning of the period	(48,245)	(19,819)
Other comprehensive loss before reclassification	(9,897)	(29,689)
Amount reclassified from accumulated other comprehensive income	3,606	1,263
Net current period other comprehensive loss	(6,291)	(28,426)
Balance at the end of the period	$ (54,536)	$ (48,245)	$ (19,819)