Derivative Instruments and Hedging Activities - Fair Value of Derivative Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Interest Rate Swaps
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Assets, Fair Value	$ 20,688	$ 5,930
Derivative Liabilities, Fair Value	1,924	5,058
Other Assets | Derivative Designated as Cash Flow Hedges | Interest Rate Swaps
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Assets, Fair Value	3,859	816
Other Assets | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Assets, Fair Value	18,754	8,936
Other Assets | Not Designated as Hedging Instrument | Residential Mortgage Loan Commitments
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Assets, Fair Value	122	60
Other Assets | Not Designated as Hedging Instrument | Interest Rate Swaps
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Assets, Fair Value	18,596	8,776
Other Assets | Not Designated as Hedging Instrument | Credit Contract
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Assets, Fair Value	36	100
Other Liabilities | Derivative Designated as Cash Flow Hedges | Interest Rate Swaps
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Liabilities, Fair Value	0	1,140
Other Liabilities | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Liabilities, Fair Value	15,684	8,934
Other Liabilities | Not Designated as Hedging Instrument | Residential Mortgage Loan Commitments
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Liabilities, Fair Value	0	0
Other Liabilities | Not Designated as Hedging Instrument | Interest Rate Swaps
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Liabilities, Fair Value	15,653	8,897
Other Liabilities | Not Designated as Hedging Instrument | Credit Contract
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Liabilities, Fair Value	$ 31	$ 37