Share-Based Compensation - Schedule of Deferred Stock Units to be Settled in Shares (Detail) - $ / shares		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019		Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Beginning balance of Outstanding, Deferred Stock Units to be Settled in Shares	[1]	73,095	76,023		76,023
Granted, Deferred Stock Units to be Settled in Shares		0	0		0
Vested, Deferred Stock Units to be Settled in Shares		0	(2,928)	[2]	0
Forfeited, Deferred Stock Units to be Settled in Shares		0	0		0
Ending balance of Outstanding, Deferred Stock Units to be Settled in Shares	[1]	73,095	73,095		76,023
Beginning balance of Outstanding, Weighted Average Grant-Date Fair Value Per Unit	[1]	$ 4.39	$ 4.44		$ 4.44
Granted, Weighted Average Grant-Date Fair Value Per Unit		0	0		0
Vested, Weighted Average Grant-Date Fair Value Per Unit		0	5.56	[2]	0
Forfeited, Weighted Average Grant-Date Fair Value Per Unit		0	0		0
Ending balance of Outstanding, Weighted Average Grant-Date Fair Value Per Unit	[1]	$ 4.39	$ 4.39		$ 4.44

[1] Includes vested but unreleased awards. These awards are included in total outstanding awards until they are released under the terms of the agreement.

[2] Includes previously vested awards which were released during the period.