Treasury Stock - Additional Information (Detail) (USD $)	6 Months Ended
	Jun. 30, 2013	May 31, 2013	Dec. 31, 2012	Dec. 31, 2010
Equity [Abstract]
Treasury stock, shares acquired	80,000
Weighted average purchase price per share	$ 187.03
Total cost of treasury shares acquired	$ 15,000,000
Treasury stock, shares	325,000		245,000
Treasury stock, purchase price per share	$ 100.57
Treasury stock, at cost	$ 32,700,000		$ 17,734,000
Repurchased shares of common stock, shares		350,000
Common stock remaining authorized for repurchase	375,000			25,000
Repurchase program expiration date	May 21, 2016