Stock-based Compensation Plans - Internal Performance Activities (Parenthetical) (Detail) - Performance-based PS-PSUs and RS-PSUs - shares		1 Months Ended	9 Months Ended
		Mar. 31, 2018	Sep. 30, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares vested and issued related to performance period number of common stock	[1]		306,978
March 2018 Grant
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Actual payout of shares		137.00%
Shares vested and issued related to performance period number of common stock		290,140
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Potential payout of shares granted			0.00%
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Potential payout of shares granted			200.00%

[1] For certain of the PS-PSUs and RS-PSUs awards issued during 2018 the aggregate payout was approximately 137% of target for the March 2018 grants with a positive performance adjustment of 290,140 shares.