Stock-based Compensation Plans - TSR - PSUs Activities (Parenthetical) (Detail) - Performance Based TSR - PSUs	3 Months Ended
	Mar. 31, 2019 shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares vested and issued related to performance period number of common stock	12,283	[1]
February 2016 Grant
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Return on common stock percentile	20.00%
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 12,283 TSR-PSUs awards issued related to the 2016 performance period where the return on our common stock was in the 20^th percentile for the February 2016 grant.  The remaining February 2016 awards are considered to be forfeited