Basis of Presentation - Stock Options Outstanding (Detail) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Stock Options:
Outstanding at beginning of period, Shares	335,730	416,886
Granted, Shares	122,357	32,830
Exercised, Shares	(22,283)	(1,815)
Outstanding at end of period, Shares	435,804	447,901
Exercisable at end of period, Shares	197,943	337,764
Weighted-average fair value of awards granted, Shares	$ 10.32	$ 12.38
Outstanding at beginning of period, Weighted-Average Exercise Price	$ 42.14	$ 43.52
Granted, Weighted-Average Exercise Price	$ 47.50	$ 40.89
Exercised, Weighted-Average Exercise Price	$ 31.36	$ 24.94
Outstanding at end of period, Weighted-Average Exercise Price	$ 44.19	$ 43.41
Exercisable at end of period, Weighted-Average Exercise Price	$ 44.52	$ 45.00