Treasury Stock and Share Based Awards - Additional Information (Detail) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2015 USD ($) $ / shares shares
Stockholders Equity Note [Line Items]
Actual cumulative forfeitures (in units) | shares	19,934
Restricted Stock
Stockholders Equity Note [Line Items]
Shares of Restricted Stock, Granted | shares	226,212
Market value of common stock on the date of grant	$ 42.79
Minimum forfeiture rate for restricted stock awards	0.00%
Maximum forfeiture rate for restricted stock awards	10.00%
Unrecognized compensation expense | $	$ 14,356
Remaining Compensation Expense recognition period (in years)	2 years
Restricted Stock | Director
Stockholders Equity Note [Line Items]
Award vesting period for restricted stock granted	1 year
Restricted Stock | Minimum
Stockholders Equity Note [Line Items]
Market value of common stock on the date of grant	$ 40.75
Restricted Stock | Minimum | Employees
Stockholders Equity Note [Line Items]
Award vesting period for restricted stock granted	1 year
Restricted Stock | Maximum
Stockholders Equity Note [Line Items]
Market value of common stock on the date of grant	$ 43.28
Restricted Stock | Maximum | Employees
Stockholders Equity Note [Line Items]
Award vesting period for restricted stock granted	4 years
Restricted Stock Units (RSUs)
Stockholders Equity Note [Line Items]
Unrecognized compensation expense | $	$ 6,040
Remaining Compensation Expense recognition period (in years)	2 years
Number of hypothetical shares of common stock | shares	142,922
Percentage of IRR, which is the threshold	7.50%
Percentage of IRR, which is the target	9.50%
Percentage of IRR, which is the maximum	11.50%
Number of hypothetical shares of common stock at assumed IRR level | shares	544,081
Restricted Stock Units (RSUs) | 2012 Grants
Stockholders Equity Note [Line Items]
Assumed IRR for grant	11.10%
Restricted Stock Units (RSUs) | Minimum
Stockholders Equity Note [Line Items]
Market value of common stock on the date of grant	$ 40.75
Expected forfeiture rate	0.00%
Restricted Stock Units (RSUs) | Maximum
Stockholders Equity Note [Line Items]
Market value of common stock on the date of grant	$ 43.28
Expected forfeiture rate	5.00%