Fair Value Accounting - Gains and Losses from Fair Value Changes Included in Consolidated Statement of Operations (Detail) $ in Thousands		3 Months Ended			9 Months Ended
		Sep. 30, 2020 USD ($)		Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)		Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Subordinated Debt Obligations, Fair Value Disclosure		$ 60,529	[1]		$ 60,529	[1]		$ 61,685	[2]
Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Unrealized Gain (Loss) Arising During Period, after Tax		$ (2,681)		$ (598)	$ (871)		$ (6,664)
Junior Subordinated Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Instrument, Measurement Input		0.0365			0.0365			0.0509
Fair Value, Liability, Recurring Basis, Still Held, Unrealized Gain (Loss)		$ (3,555)		794	$ 1,156		(8,837)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Other Comprehensive Income (Loss)	[3]	$ (3,555)		$ 794	$ 1,156		$ (8,837)
Period of basis point spread					3.42%		3.18%
Percentage of LIBOR					0.23%		1.91%

[1] Includes only the portion of junior subordinated debt that is recorded at fair value at each reporting period pursuant to the election of FVO treatment.

[2] Includes only the portion of junior subordinated debt that is recorded at fair value at each reporting period pursuant to the election of FVO treatment.

[3] Unrealized gains/(losses) attributable to changes in the fair value of junior subordinated debt are recorded as part of OCI, net of tax, and totaled $(2.7) million and $0.6 million for three months ended September 30, 2020 and 2019, respectively, and $0.9 million and $(6.7) million for the nine months ended September 30, 2020 and 2019, respectively.