Stock-Based Compensation Plans - PSUA Activity (Parenthetical) (Detail)	3 Months Ended	9 Months Ended
	Mar. 31, 2014	Sep. 30, 2015
Performance Shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period	3 years	3 years
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Actual payout of shares on performance units granted		0.00%
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Actual payout of shares on performance units granted		150.00%