Derivatives and Hedging Additional Information (Detail) - USD ($)	3 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2018
Derivative [Line Items]
Gain (Loss) on Foreign Currency Derivative Instruments Not Designated as Hedging Instruments	$ 1,000,000.0	$ 2,300,000	$ 1,200,000	$ 2,400,000
Collateral netted against derivative liabilities	62,800,000		39,800,000		$ 44,900,000
Over collateralization net position	20,300,000		11,600,000		7,600,000
Additional collateral held in securities	83,100,000
Derivative, Amount of Hedged Item, Loans	678,369,000				650,428,000
Fair Value Hedge Assets, Loans	58,355,000				23,039,000
Derivative, Amount of Hedged Item	(316,392,000)				(299,401,000)
Hedged Liability, Fair Value Hedge, Cumulative Increase (Decrease)	2,963,000				19,691,000
Subordinated Debentures Maturing July 2025 [Member] | Subordinated Debt [Member]
Derivative [Line Items]
Debt Instrument, Face Amount	150,000,000.0
Subordinated Debentures Maturing July 2056 [Member] | Subordinated Debt [Member]
Derivative [Line Items]
Debt Instrument, Face Amount	175,000,000.0
Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Liability, Fair Value	62,754,000		41,015,000		44,892,000
Negative NPVs	$ 62,591,000		$ 37,177,000		$ 42,730,000