Summary of Company's Treasury Stock Activity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013
Schedule Of Stock Options [Line Items]
Beginning Balance, Shares	3,553,085
Restricted stock withholdings	112,251	[1]
Ending Balance, Shares	3,665,336
Beginning Balance, Cost	$ 48,482
Restricted stock withholdings	3,254	[1]
Ending Balance, Cost	$ 51,736

[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. The Company determined the number of shares to be withheld based upon market values ranging from $27.19 to $29.44 per share.