Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			$ (32,616)
Personnel expense	$ (103,819)	$ (101,134)	(307,346)	$ (304,272)
Interest income (Amortization of net unrealized gains on available for sale securities transferred to held to maturity securities)	(1,441)	0	(4,465)	0
Total other comprehensive income (loss)	14,707	(12,782)	(31,362)	(20,226)
Ending Balance	(1,254)		(1,254)
Investment Securities Available For Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	45,916	25,282	459	18,512
Other comprehensive income (loss) before reclassifications	(22,894)	22,907	59,849	35,101
Investment securities gain (loss), net	13	(2,796)	(6,201)	(4,038)
Personnel expense	0	0	0	0
Interest income (Amortization of net unrealized gains on available for sale securities transferred to held to maturity securities)	(1,441)		(4,465)
Income tax (expense) benefit	9,280	(7,725)	(18,768)	(11,907)
Total other comprehensive income (loss)	15,042	(12,386)	(30,415)	(19,156)
Ending Balance	30,874	37,668	30,874	37,668
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(32,463)	(22,688)	(33,075)	(23,362)
Other comprehensive income (loss) before reclassifications	0	0	0	0
Investment securities gain (loss), net	0	0	0	0
Personnel expense	541	639	1,531	1,729
Interest income (Amortization of net unrealized gains on available for sale securities transferred to held to maturity securities)	0		0
Income tax (expense) benefit	(206)	(243)	(584)	(659)
Total other comprehensive income (loss)	(335)	(396)	(947)	(1,070)
Ending Balance	(32,128)	(22,292)	(32,128)	(22,292)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	13,453	2,594	(32,616)	(4,850)
Other comprehensive income (loss) before reclassifications	(22,894)	22,907	59,849	35,101
Investment securities gain (loss), net	13	(2,796)	(6,201)	(4,038)
Personnel expense	541	639	1,531	1,729
Interest income (Amortization of net unrealized gains on available for sale securities transferred to held to maturity securities)	(1,441)		(4,465)
Income tax (expense) benefit	9,074	(7,968)	(19,352)	(12,566)
Total other comprehensive income (loss)	14,707	(12,782)	(31,362)	(20,226)
Ending Balance	$ (1,254)	$ 15,376	$ (1,254)	$ 15,376