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, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net securities gains									$ (1,923)	$ (2,060)	$ (9,135)
Interest income (expense)	$ (148,899)	$ (153,096)	$ (155,230)	$ (147,048)	$ (146,225)	$ (130,842)	$ (131,963)	$ (128,572)	(604,273)	(537,602)	(437,168)
Salaries and employee benefits									(30)	(191)	(159)
Income tax (expense) benefit	11,433	13,254	14,359	13,104	3,223	5,325	4,345	4,957	52,150	17,850	72,939
Net income	$ (49,185)	$ (69,781)	$ (62,964)	$ (56,276)	$ (47,498)	$ (51,348)	$ (44,001)	$ (47,983)	(238,206)	(190,830)	(95,725)
Gains and Losses on Cash Flow Hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period									449	(113)	(3,803)
Unrealized Gains and Losses on Available- for-Sale Debt Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period									1,485	1,662	6,160
Accumulated Unrealized Gains and Losses on Held-to-Maturity Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period									(2,096)	(1,678)	(1,203)
Defined Benefit Pension Plans [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period									(22)	(144)	(64)
Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period									(184)	(273)	1,090
Reclassifications out of Accumulated Other Comprehensive Income (Loss) [Member] | 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)									596	(150)	(6,135)
Income tax (expense) benefit									(147)	37	2,332
Net income									449	(113)	(3,803)
Reclassifications out of Accumulated Other Comprehensive Income (Loss) [Member] | Unrealized Gains and Losses on Available- for-Sale Debt Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net securities gains									1,923	2,060	9,135
Income tax (expense) benefit									(438)	(398)	(2,975)
Net income									1,485	1,662	6,160
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)									(2,812)	(2,181)	(1,830)
Income tax (expense) benefit									716	503	627
Net income									(2,096)	(1,678)	(1,203)
Reclassifications out of Accumulated Other Comprehensive Income (Loss) [Member] | Defined Benefit Pension Plans [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Salaries and employee benefits									(30)	(191)	(159)
Income tax (expense) benefit									8	47	95
Net income									$ (22)	$ (144)	$ (64)