Changes and Reclassifications Out of Accumulated Other Comprehensive Income (Schedule of Accumulated Other Comprehensive Income) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amortization of prior service cost reclassified to other noninterest expense, before Tax	$ 410
Amortization of prior service cost reclassified to other noninterest expense, Tax	143	0
Amortization of prior service cost reclassified to other noninterest expense, Net of Tax	267	0
Accumulated Other Comprehensive Income (Loss), before Tax	(75,792)	(85,390)
accumulated other comprehensive income, tax	(26,525)	(29,886)
Accumulated other comprehensive loss	(49,267)	(55,504)	(71,892)
Changes in unrealized securities' holding gains/(losses), before Tax	34,117	18,044
Changes in unrealized securities' holding gains/(losses), Tax	11,941	6,315
Changes in unrealized securities' holding gains/(losses), Net of Tax	22,176	11,729
Changes in unrealized securities' holding gains/(losses) that result from securities being transferred from available-for-sale to held-to-maturity, before Tax	(504)	(494)
Changes in unrealized securities' holding gains/(losses) that result from securities being transferred from available-for-sale to held-to-maturity, Tax	(176)	(173)
Changes in unrealized securities' holding gains/(losses) that result from securities being transferred from available-for-sale to held-to-maturity , Net of Tax	(328)	(321)
Net losses/(gains) realized on sale of securities reclassified to noninterest income, before Tax	(354)	(56)
Net losses/(gains) realized on sale of securities reclassified to noninterest income, Tax	(124)	(20)
Net losses/(gains) realized on sale of securities reclassified to noninterest income, Net of Tax	(230)	(36)
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax	(100,520)	(57,812)	(102,068)	(57,812)
Accumulated other comprehensive income reclassifications, benefit plan, tax	(35,181)	(20,233)	(35,722)	(20,233)
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	(65,339)	(37,579)	(66,346)	(37,579)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, Net of Tax		0
Amortization of actuarial losses/(gains), before Tax	1,138
Amortization of actuarial losses/(gains), Tax	398	0
Amortization of actuarial losses/(gains), Net of Tax	740
Accumulated Net Unrealized Investment Gain (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), before Tax	24,728	(27,578)	(8,531)	(45,072)
accumulated other comprehensive income, tax	8,656	(9,653)	(2,985)	(15,775)
Accumulated other comprehensive loss	$ 16,072	$ (17,925)	$ (5,546)	$ (29,297)