Treasury Stock and Share Based Awards - Additional Information (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Stockholders Equity Note [Line Items]
Intrinsic value of options exercised	$ 168
Average remaining contractual life of options outstanding	1 year
Tax benefit recognized on stock option exercised	71
Total fair value of vested shares	13,440
Tax benefit recognized on vested shares	4,268
Restricted Stock
Stockholders Equity Note [Line Items]
Shares of Restricted Stock Granted	220,526
Market value of common stock on the date of grant	$ 29.28
Minimum forfeiture rate for restricted stock awards	0.00%
Maximum forfeiture rate for restricted stock awards	5.00%
Compensation expense	7,823	8,004
Unrecognized compensation expense	16,850
Weighted average period over which remaining compensation expense will be recognized (in years)	2 years
Shares of restricted stock, forfeited	21,847
Restricted stock awards vested	461,060
Restricted Stock | Director
Stockholders Equity Note [Line Items]
Award vesting period for restricted stock granted	1 year
Restricted Stock | Employee Scenario One
Stockholders Equity Note [Line Items]
Award vesting period for restricted stock granted	3 years
Restricted Stock | Employee Scenario Two
Stockholders Equity Note [Line Items]
Award vesting period for restricted stock granted	4 years
Restricted Stock | Minimum
Stockholders Equity Note [Line Items]
Market value of common stock on the date of grant	$ 27.92
Restricted Stock | Maximum
Stockholders Equity Note [Line Items]
Market value of common stock on the date of grant	$ 29.44
Restricted Stock Units (RSUs)
Stockholders Equity Note [Line Items]
Market value of common stock on the date of grant	$ 29.44
Unrecognized compensation expense	4,602
Weighted average period over which remaining compensation expense will be recognized (in years)	1 year
Number of hypothetical shares of common stock issued to employees	115,107
Percentage of IRR, which is the threshold	8.50%
Percentage of IRR, which is the target	10.50%
Percentage of IRR, which is the maximum	12.50%
Percentage of restricted stock units vest	100.00%
Expected forfeiture rate	5.00%
Shares of restricted stock, forfeited	11,498
Compensation expense	2,523	2,161
Restricted stock awards vested	295,751
Restricted stock unit conversion into share of common stock, conversion ratio	1
Dividends paid on vested restricted stock units	939
Total fair value of shares vested during the period	8,723
Recognized tax benefits related to shares vested during the period	$ 3,663
Number of hypothetical shares of common stock	802,529
Actual cumulative forfeitures (in units)	11,498