Stock Option Plans - Summary of Option Activity (Detail) (USD $)	6 Months Ended
	Jun. 30, 2014
Number of Shares
Outstanding at beginning of period (in shares)	753,625
Granted (in shares)	200,000
Exercised (in shares)	(99,685)
Expired/Forfeited (in shares)	(37,500)
Outstanding at end of period (in shares)	816,440
Exercisable at end of period (in shares)	448,940
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)	$ 37.23
Expired/Forfeited (in usd per share)	$ 43.56
Outstanding at end of period (in usd per share)	$ 44.26
Exercisable at end of period (in usd per share)	$ 43.87
Aggregate intrinsic value
Outstanding at beginning of period	$ 4,529,206
Granted	314,000
Exercised	1,018,511
Expired/Forfeited
Outstanding at end of period	4,078,348
Exercisable at end of period	$ 2,659,611