Acquisitions - Additional Information (Detail)		3 Months Ended		12 Months Ended
	Jan. 04, 2019 USD ($) Branch $ / shares shares	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Business Acquisition, Contingent Consideration [Line Items]
Goodwill				$ 156,277,000	$ 136,433,000
Merger and acquisition integration-related expenses				3,178,000	464,000	$ 0
Highlands Bancorp, Inc.
Business Acquisition, Contingent Consideration [Line Items]
Goodwill	$ 19,844,000
Number of bank branches operated | Branch	4
Conversion ratio (in shares) | shares	1.015
Consideration paid through common stock (in shares) | shares	2,837,524
Stock option payout price per share (in dollars per share) | $ / shares	$ 14.71
Average strike price (usd per share) | $ / shares	$ 8.09
Cash paid in connection with cancellation of the old stock options	$ 797,000
Goodwill adjustments		$ 447,000,000	$ 1,700,000
Finite-lived intangible asset, useful life	10 years
Identifiable intangible assets	$ 3,728,000
Merger and acquisition integration-related expenses				$ 3,200,000	$ 464,000	$ 0