Accumulated Other Comprehensive Income (Loss) Reclassifications Out of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	$ 24,800	$ (11,577)	$ (4,850)	$ (24,244)
Other Comprehensive Income before reclassifications	(35,224)	35,557	12,194	56,184
Amounts reclassified from accumulated other comprehensive income (loss)	(697)	297	(152)	250
Income tax expense	13,715	(13,783)	(4,598)	(21,696)
Total other comprehensive income (loss)	(22,206)	22,071	7,444	34,738
Ending Balance	2,594	10,494	2,594	10,494
Securities Available For Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	47,825	1,067	18,512	(11,396)
Other Comprehensive Income before reclassifications	(35,224)	35,557	12,194	56,184
Amounts reclassified from accumulated other comprehensive income (loss)	(1,242)	(34)	(1,242)	(412)
Income tax expense	13,923	(13,655)	(4,182)	(21,441)
Total other comprehensive income (loss)	(22,543)	21,868	6,770	34,331
Ending Balance	25,282	22,935	25,282	22,935
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(23,025)	(12,644)	(23,362)	(12,848)
Other Comprehensive Income before reclassifications	0	0	0	0
Amounts reclassified from accumulated other comprehensive income (loss)	545	331	1,090	662
Income tax expense	(208)	(128)	(416)	(255)
Total other comprehensive income (loss)	337	203	674	407
Ending Balance	$ (22,688)	$ (12,441)	$ (22,688)	$ (12,441)