Derivative Instruments and Hedge Activities - Summary of Company's Interest Rate Derivative and Offsetting Positions (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Gross amounts recognized	$ 13,620	$ 5,981
Net amount presented in the Consolidated Statements of Financial Condition	13,620	5,981
Gross amounts not offset in the Consolidated Statements of Financial Condition
Offsetting derivative positions	(757)	(232)
Collateral posted	(12,863)	(5,371)
Net credit exposure	0	378
Gross amounts recognized	2,769	994
Net amount presented in the Consolidated Statements of Financial Condition	2,769	994
Gross amounts not offset in the Consolidated Statements of Financial Condition
Offsetting derivative positions	(757)	(232)
Collateral posted	(2,007)	(745)
Net credit exposure	$ 5	$ 17