Stock-based Compensation Plans - PS/RS-PSUs Activities (Parenthetical) (Detail) - Performance-based PS-PSUs and RS-PSUs - shares		1 Months Ended		6 Months Ended
		May 31, 2017	Mar. 31, 2017	Jun. 30, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares vested and issued related to performance period number of common stock	[1]			101,150
March 2017 Grant
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Aggregate payout of shares issued			150.00%
Shares vested and issued related to performance period number of common stock		58,591
May 2017 Grant
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Aggregate payout of shares issued				150.00%
Shares vested and issued related to performance period number of common stock				58,591
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 the PS-PSUs and RS-PSUs awards issued during 2017 the aggregate payout was approximately 150% of target for the March 2017 and May 2017 grants with a positive performance adjustment of 58,591 shares