Estimated Fair Value of Financial Instruments and Fair Value Measurement - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Subordinate debt	$ 104,995	$ 104,902
Non-rated
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term municipal bond	5,400
Subordinate debt	$ 1,000
Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rates	5.00%
Capitalization rates	4.00%
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rates	11.00%
Capitalization rates	9.00%