Stockholder's Equity - Additional Information (Detail) (USD $)	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Stockholders' Equity Note [Abstract]
Common stock reserved and available for issuance	1,500,000
Percentage of directors' stock grant vested on one year anniversary date	100.00%
Period of Vested Shares	5 years
Granted, Weighted average grant date fair value	$ 23.59
Share based award, settled in cash	2,600
Total unrecognized compensation cost related to nonvested shares of common stock granted	$ 9,000,000
Weighted average period of cost recognized	3 years 3 months 1 day
Total fair value of shares of common stock vested	3,900,000	3,800,000
Compensation expense related to nonvested stock grants	3,100,000	2,900,000
Price of shares issued under Employee Stock Purchase Plan as a percentage of FMV	95.00%
Number of shares reserved for the Employee Stock Purchase Plan	250,000
Additional shares authorized for issuance	250,000
Stock options issued and exercisable	15,000
Options exercised	0
Options granted	0
Shares redeemed to satisfy personal tax obligations	39,785
Treasury shares redeemed to pay income tax	$ 923,000
Share based payment description	The amount of such cash payment will equal the fair market value of 2,600 shares on the settlement date.
Options forfeited	0
Director
Stockholders' Equity Note [Abstract]
Non vested stock grants to Independent director	26,900
Director Period of Vested Shares	1 year
Employee
Stockholders' Equity Note [Abstract]
Nonvested stock grants to employees	172,545