Comprehensive Income - Reclassifications out of AOCI (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest on investment securities held to maturity		$ 6,639	$ 6,795
Interest and fees on loans		574,712	561,083
Interest and fees on FHLB advances		(19,068)	(18,012)
Net income before income tax expense		166,669	64,698
Income tax (expense) benefit		(45,846)	(25,431)
Net income		120,823	39,267
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Unrealized Gains (Losses) on Securities Available for Sale and Transferred to Held to Maturity
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment securities gains, net	[1]	0	8,353
Interest on investment securities held to maturity	[1]	(1,058)	(835)
Net income before income tax expense	[1]	(1,058)	7,518
Income tax (expense) benefit	[1]	392	(2,753)
Net income	[1]	(666)	4,765
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Accumulated Gains (Losses) on Cash Flow Hedging Instruments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest and fees on loans	[1]	6,374	2,048
Interest and fees on FHLB advances	[1]	(680)	(1,529)
Net income before income tax expense	[1]	5,694	519
Income tax (expense) benefit	[1]	(2,113)	(190)
Net income	[1]	3,581	329
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Defined Benefit Plan Adjustment
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net periodic expense	[1],[2]	773	(1,300)
Income tax (expense) benefit	[1]	(288)	369
Net income	[1]	485	(931)
Reclassification out of Accumulated Other Comprehensive Income (Loss) | Unamortized Impairment Losses on Investment Securities Held to Maturity
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest on investment securities held to maturity	[1]	(354)	(351)
Income tax (expense) benefit	[1]	131	129
Net income	[1]	$ (223)	$ (222)

[1] Amounts in parentheses indicate debits to the consolidated statement of income.

[2] These accumulated other comprehensive income components are included in the computation of net periodic pension cost (see Note 19, Benefit Plans, in the Notes to the December 31, 2016, Consolidated Financial Statements for additional details).