Accumulated Other Comprehensive Income (Loss) - Reclassifications out of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net securities gains									$ 5,848	$ 5,718	$ 9,830
Interest income/(expense)	$ 109,917	$ 107,803	$ 99,340	$ 85,643	$ 85,922	$ 97,104	$ 92,097	$ 90,993	402,703	366,116	366,370
Salaries and employee benefits, Actuarial gains/(losses) and settlement cost									11,203	3,002	(4,333)
Impairment losses											(100)
Income before income taxes									(5,848)	(5,718)	(9,830)
Income tax (expense) benefit	(14,710)	(10,969)	(30,812)	(9,671)	(11,598)	(16,395)	(8,959)	(9,225)	(66,162)	(46,177)	(38,297)
Net income	$ 33,456	$ 34,709	$ 39,122	$ 26,977	$ 31,985	$ 37,669	$ 26,156	$ 20,906	134,264	116,716	103,667
Reclassifications out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income									(8,378)	(1,231)	7,581
Reclassifications out of Accumulated Other Comprehensive Income (Loss) [Member] | Accumulated Unrealized Gains and Losses on Available-for-Sale Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net securities gains									5,848	5,718	9,830
Impairment losses											(100)
Income before income taxes									5,848	5,718	9,730
Income tax (expense) benefit									(2,155)	(2,106)	(3,699)
Net income									3,693	3,612	6,031
Reclassifications out of Accumulated Other Comprehensive Income (Loss) [Member] | Accumulated Unrealized Gains and Losses on Held-to-Maturity Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income/(expense)									(1,776)	(1,692)	(1,437)
Income tax (expense) benefit									606	396	446
Net income									(1,170)	(1,296)	(991)
Reclassifications out of Accumulated Other Comprehensive Income (Loss) [Member] | Accumulated Gains and Losses on Cash Flow Hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax (expense) benefit									2,452	1,033	94
Net income									(4,001)	(1,686)	(154)
Reclassifications out of Accumulated Other Comprehensive Income (Loss) [Member] | Accumulated Gains and Losses on Cash Flow Hedges [Member] | Interest Rate Contracts [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income/(expense)									(6,453)	(2,719)	(248)
Reclassifications out of Accumulated Other Comprehensive Income (Loss) [Member] | Accumulated Defined Benefit Pension Plans [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Salaries and employee benefits, Actuarial gains/(losses) and settlement cost									(11,203)	(3,002)	4,333
Income tax (expense) benefit									4,303	1,141	(1,638)
Net income									$ (6,900)	$ (1,861)	$ 2,695