Derivative Instruments and Hedging Activities - Fair Value of Company's Derivative Financial Instruments Classification on Unaudited Condensed Consolidated Balance Sheets (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Derivatives Fair Value [Line Items]
Asset Derivatives Fair Value	$ 6,774
Liability Derivatives Fair Value		$ 8,455
Other Assets [Member]
Derivatives Fair Value [Line Items]
Asset Derivatives Fair Value	6,800
Other Liabilities [Member]
Derivatives Fair Value [Line Items]
Liability Derivatives Fair Value		8,500
Interest Rate Swaps [Member] | Other Assets [Member]
Derivatives Fair Value [Line Items]
Asset Derivatives Fair Value	$ 6,774
Interest Rate Swaps [Member] | Other Liabilities [Member]
Derivatives Fair Value [Line Items]
Liability Derivatives Fair Value		$ 8,455