Fair Value Accounting - Gains and Losses from Fair Value Changes Included in Consolidated Statement of Operations (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Subordinated Debt Obligations, Fair Value Disclosure	$ 56,546		$ 48,684
Unrealized (loss) gain on junior subordinated debt, net of tax effect of $1,934 and $(478), respectively	$ (5,928)	$ 1,466
Junior Subordinated Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Instrument, Measurement Input	0.06645		0.07820
Fair Value, Liabilities Measured on Recurring Basis, Change in Unrealized Gain (Loss)	$ (7,862)	$ 1,944
Period of basis point spread	4.05%	5.01%
Percentage of LIBOR	2.60%	2.81%