Summary of Treasury Stock Activity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	6 Months Ended
	Jun. 30, 2013
Schedule Of Stock Options [Line Items]
Beginning Balance, Shares	3,553,085
Restricted stock withholdings	119,197	[1]
Restricted stock forfeitures	11,381
Ending Balance, Shares	3,683,663
Beginning Balance, Cost	$ 48,482
Restricted stock withholdings	3,464	[1]
Restricted stock forfeitures	0
Ending Balance, Cost	$ 51,946

[1] The Company withheld restricted shares as a result of the election by certain employees to satisfy their tax liabilities upon vesting in restricted stock and restricted stock units. The Company determined the number of shares to be withheld based upon market values ranging from $27.19 to $30.23 per share.