Treasury Stock - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Equity [Abstract]
Treasury stock, shares acquired	60,000
Weighted average purchase price per share	$ 172.55
Total cost of treasury shares acquired	$ 10,400,000
Repurchased shares of common stock, shares	305,000	245,000
Repurchased shares of common stock, value	$ 28,090,000	$ 17,734,000
Average price of per share	$ 92.05
Common stock remaining authorized for repurchase	45,000