Fair Value of Performance Units (Detail) - Performance Units Awards $ in Thousands	6 Months Ended
	Jun. 30, 2021 USD ($)
2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Aggregate fair value at date of grant	$ 7,225
2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Aggregate fair value at date of grant	826
2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Aggregate fair value at date of grant	9,958
2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Aggregate fair value at date of grant	8,004
2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Aggregate fair value at date of grant	$ 5,780