Stock Option Plans - Summary of Option Activity (Detail) (USD $)	3 Months Ended
	Mar. 31, 2014
Number of Shares
Outstanding at beginning of period (in shares)	753,625
Granted (in shares)	0
Exercised (in shares)	(31,600)
Expired/Forfeited (in shares)	0
Outstanding at end of period (in shares)	722,025
Exercisable at end of period (in shares)	381,400
Weighted average exercise price per share
Outstanding at beginning of period (in usd per share)	$ 42.55
Granted (in usd per share)	$ 0.00
Exercised (in usd per share)	$ 29.39
Expired/Forfeited (in usd per share)	$ 0.00
Outstanding at end of period (in usd per share)	$ 43.14
Exercisable at end of period (in usd per share)	$ 43.49
Aggregate intrinsic value
Outstanding at beginning of period	$ 4,529,206
Granted	0
Exercised	555,959
Expired/Forfeited	0
Outstanding at end of period	3,724,265
Exercisable at end of period	$ 2,150,234