Summary of Significant Accounting Policies (Narrative) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption		$ (2,285)
Gross interchange and debit card transaction fees	$ 25,769
Gross cost related to interchange and debit card transactions	11,892	11,943	$ 12,896
Interchange and debit card transaction fees	13,877	23,232	$ 21,369
Cash on hand or on deposit required	195,200	179,600
Cash collateral on deposit	10,000	19,600
Foreclosed Assets	$ 1,200	2,100
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]
Reclassification of certain income tax effects related to U.S. statutory federal income tax rate under the Tax Cuts and Jobs Act	$ (9,535)
Cumulative Effect of New Accounting Principle in Period of Adoption		$ (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	$ 9,535