Stock-based Compensation Plans - PSUA Activities (Detail) - Market-based TSR - $ / shares		3 Months Ended
		Mar. 31, 2017		Mar. 31, 2016
Summary of Market-based TSR Awards outstanding, Number of Units
Outstanding, Beginning Balance		395,908
Granted	[1]	83,247
Vested		(61,943)
Forfeited		(3,679)
Outstanding, Ending Balance		413,533
Summary of Market-based TSR Awards outstanding, Weighted Average Grant Date Fair Value
Outstanding, Beginning Balance, weighted average grant date fair value		$ 44.39
Granted, weighted average grant date fair value		28.31	[1]	$ 30.47
Vested, weighted average grant date fair value		51.20
Forfeited, weighted average grant date fair value		44.21
Outstanding, Ending Balance, weighted average grant date fair value		$ 40.14

[1] Amounts granted reflect the number of performance units granted; however, the actual payout of shares will be between zero and 150% of the performance units granted depending on the total shareholder return ranking compared to the peer companies at the end of the three-year performance period.