Stock-based Compensation Plans - TSR - PSUs Activities (Parenthetical) (Detail) - Performance Based TSR - PSUs	12 Months Ended
	Dec. 31, 2020 shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares vested and issued related to performance period number of common stock	278,184	[1]
March 2017 Grant
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Return on common stock percentile	60.00%
May 2017 Grant
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Return on common stock percentile	80.00%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Potential payout of shares on performance units granted	0.00%
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Potential payout of shares on performance units granted	200.00%

[1] Includes 278,184 TSR-PSUs awards issued related to 2017 performance where the return on our common stock was in the 60^th percentile for the March 2017 grant and the 80^th percentile for the May 2017 grant. The remaining 2017 awards were considered to be forfeited.