Quarterly Financial Information - Summary of Quarterly Data (Parenthetical) (Detail)	1 Months Ended	3 Months Ended			12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2017 USD ($) Loan	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Merger related expenses					$ 5,001,000	$ 787,000
Other asset impairment charge		$ 2,300,000
Number of development loans | Loan		2
Charges awarded to another claimant as per appellate court ruling	$ 2,300,000
Tax Cuts And Jobs Act Of 2017 Change In Tax Rate Income Tax Expense Benefit		$ 1,500,000			1,500,000
OLCB [Member]
Merger related expenses			$ 5,000,000	$ 787,000	$ 368,000