Stock-based Compensation Plans - TSR - PSUs Activities (Parenthetical) (Detail) - Performance Based TSR - PSUs - shares	12 Months Ended
	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
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]	73,985	[2]	85,461	[3]
February 2014 Grant
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Return on common stock percentile					67.00%
May 2014 Grant
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Return on common stock percentile					56.00%
February 2015 Grant
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Return on common stock percentile			46.00%
May 2015 Grant
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Return on common stock percentile			36.00%
February 2016 Grant
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Return on common stock percentile	20.00%
May 2016 Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of awards forfeited	100.00%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Potential payout of shares on performance units granted	0.00%		0.00%		0.00%
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Potential payout of shares on performance units granted	200.00%		200.00%		150.00%

[1] Includes 12,283 TSR-PSUs awards issued related to 2016 performance 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. The May 2016 awards were 100% forfeited as the performance was not achieved.

[2] Includes 73,985 TSR-PSUs awards issued related to the 2015 performance period where the return on our common stock was the 46^th percentile for the February 2015 grant and the 36^th percentile for the May 2015 grant. The remaining 2015 awards are considered to be forfeited.

[3] Includes 85,461 TSR-PSU awards issued related to the 2014 performance period where the return on our common stock was the 67^th percentile for the February 2014 grant and 56^th percentile for the May 2014 grant. The remaining 2014 awards are considered to be forfeited.