Stock-Based Compensation Plans - PSUA Activities (Detail) - Performance Shares - $ / shares		3 Months Ended
		Mar. 31, 2016		Mar. 31, 2015
Summary of Performance Share Unit Awards outstanding, Number of Units
Outstanding, Beginning Balance		262,124
Granted	[1]	118,193
Vested		(42,546)
Forfeited		0
Outstanding, Ending Balance		337,771
Summary of Performance Share Unit Awards outstanding, Weighted Average Grant Date Fair Value
Outstanding, Beginning Balance, weighted average grant date fair value		$ 64.77
Granted, weighted average grant date fair value		30.47	[1]	$ 55.17
Vested, weighted average grant date fair value		60.75
Forfeited, weighted average grant date fair value		0
Outstanding, Ending Balance, weighted average grant date fair value		$ 53.28

[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.