Stock-Based Compensation Plans - PSUA Activity (Detail) - Performance Shares - $ / shares		9 Months Ended
		Sep. 30, 2015		Sep. 30, 2014
Summary of Performance Share Unit Awards outstanding, Number of Units
Outstanding, Beginning Balance		134,341
Units granted	[1]	276,204
Units vested		(103,397)
Units forfeited		(2,679)
Outstanding, Ending Balance		304,469
Summary of Performance Share Unit Awards outstanding, Weighted Average Grant Date Fair Value
Outstanding, Beginning Balance, weighted average grant date fair value		$ 86.11
Granted, weighted average grant date fair value		56.78	[1]	$ 86.14
Vested, weighted average grant date fair value		69.67
Forfeited, weighted average grant date fair value		82.60
Outstanding, Ending Balance, weighted average grant date fair value		$ 65.12

[1] Amounts granted reflect the number of performance units granted; however, the actual payout of shares will be between zero percent 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.