Compensation Expense Associated with Performance Units (Detail) - Performance Units Awards - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense associated with Performance Units	$ 602		$ 1,204
2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense associated with Performance Units	69	$ 69	206	$ 138
2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense associated with Performance Units	$ 830	830	2,489	2,489
2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense associated with Performance Units		$ 667	$ 667	2,001
2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense associated with Performance Units				$ 642