Summary of Significant Accounting Policies (Narrative) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash on hand or on deposit required	$ 918,000	$ 447,900
Cash collateral on deposit	37,500	10,000
Foreclosed assets	1,100	1,200
Operating lease, right-of-use asset	297,736	0		$ 170,500
Operating lease, liability				$ 174,400
Cumulative effect of new accounting principle in period of adoption		(14,672)	$ (2,285)
Additional premium amortization expense on securities	5,200
Gross interchange and debit card transaction fees	27,800	25,800	23,200
Gross cost related to interchange and debit card transactions	12,900	11,900	11,900
Interchange and debit card transaction fees	$ 14,873	13,877	23,232
Minimum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Range of change in fair value of derivative hedging instrument to be considered highly effective	80.00%
Maximum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Range of change in fair value of derivative hedging instrument to be considered highly effective	125.00%
Retained Earnings [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption		(14,672)	$ (2,285)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification of certain income tax effects related to U.S. statutory federal income tax rate under the Tax Cuts and Jobs Act		$ 9,500