Accumulated Other Comprehensive Income (Loss) - Reclassifications out of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net securities gains	$ (788)	$ (1,500)
Interest income (expense)	(128,572)	(105,801)
Salaries and employee benefits	(51)	(27)
Income tax (expense) benefit	4,957	10,491
Net income	(47,983)	(35,992)
Total reclassifications for Net income the period	(463)	(480)
Unrealized Gains and Losses on Available-for-Sale Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for Net income the period	593	947
Accumulated Unrealized Gains and Losses on Held-to-Maturity Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for Net income the period	(456)	(295)
Gains and Losses on Cash Flow Hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for Net income the period	(580)	(1,115)
Defined Benefit Pension Plans [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for Net income the period	(20)	(17)
Reclassifications out of Accumulated Other Comprehensive Income (Loss) [Member] | Unrealized Gains and Losses on Available-for-Sale Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net securities gains	788	1,500
Income tax (expense) benefit	(195)	(553)
Net income	593	947
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)	(591)	(449)
Income tax (expense) benefit	135	154
Net income	(456)	(295)
Reclassifications out of Accumulated Other Comprehensive Income (Loss) [Member] | Gains and Losses on Cash Flow Hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax (expense) benefit	189	684
Net income	(580)	(1,115)
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)	(769)	(1,799)
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	(51)	(27)
Income tax (expense) benefit	31	10
Net income	$ (20)	$ (17)