Accumulated Other Comprehensive Income (Loss) - Reclassifications out of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net securities gains	$ 103	$ (788)
Interest income (expense)	(147,048)	(128,572)
Salaries and employee benefits	(20)	(51)
Income tax (expense) benefit	13,104	4,957
Net income	(56,276)	(47,983)
Gains and Losses on Cash Flow Hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period	290	(580)
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	(79)	593
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	(351)	(456)
Defined Benefit Pension Plans [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period	(15)	(20)
Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income	0	0
Total reclassifications for the period	(155)	(463)
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)	385	(769)
Income tax (expense) benefit	(95)	189
Net income	290	(580)
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	(103)	788
Income tax (expense) benefit	24	(195)
Net income	(79)	593
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)	(457)	(591)
Income tax (expense) benefit	106	135
Net income	(351)	(456)
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	(20)	(51)
Income tax (expense) benefit	5	31
Net income	$ (15)	$ (20)