Stock Option Plans - Summary of Option Activity (Detail) (USD $)	9 Months Ended
	Sep. 30, 2014
Number of Shares
Outstanding at beginning of period (in shares)	753,625
Granted (in shares)	200,000
Exercised (in shares)	(131,566)
Expired/Forfeited (in shares)	(37,500)
Outstanding at end of period (in shares)	784,559
Exercisable at end of period (in shares)	417,059
Weighted average exercise price per share
Outstanding at beginning of period (in usd per share)	$ 42.55
Granted (in usd per share)	$ 47.03
Exercised (in usd per share)	$ 37.30
Expired/Forfeited (in usd per share)	$ 43.56
Outstanding at end of period (in usd per share)	$ 44.54
Exercisable at end of period (in usd per share)	$ 44.36
Aggregate intrinsic value
Outstanding at beginning of period	$ 4,529,206
Granted	0
Exercised	1,408,665
Expired/Forfeited
Outstanding at end of period	2,533,163
Exercisable at end of period	$ 1,748,675