Additional Information about Assets and Liabilities That Are Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 7,052	$ 8,121
Change in fair value of financial instruments	(1,941)	(3,010)
Ending Balance	5,111	5,111
Junior Subordinated Notes, at Fair Value
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	7,052	8,121
Change in fair value of financial instruments	(1,941)	(3,010)
Ending Balance	$ 5,111	$ 5,111