Stockholder's Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Stockholders' Equity Note [Abstract]
Common stock reserved and available for issuance	1,500,000
Common stock shares available for grant	499,037
Document Period End Date	Jun. 30, 2015
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	$ 33.80
Share based award, settled in cash	1,800
Total unrecognized compensation cost related to nonvested shares of common stock granted	$ 11,300
Weighted average period of cost recognized	3 years 3 months 1 day
Total fair value of shares of common stock vested	$ 3,900	$ 3,600
Compensation expense related to nonvested stock grants	$ 2,100
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 exercised, Shares	9,500
Options, Weighted Average Exercise Price	$ 15.21
Options granted	0
Options outstanding	5,500
Options, Outstanding, Weighted Average Exercise Price	$ 19.75
Shares redeemed to satisfy personal tax obligations	38,797
Treasury shares redeemed to pay income tax	$ 1,329
Options forfeited	0
Director
Stockholders' Equity Note [Abstract]
Non vested stock grants to Independent director	16,200
Director Period of Vested Shares	1 year
Employee
Stockholders' Equity Note [Abstract]
Nonvested stock grants to employees	174,865