Summary of Activity for Company's Restricted Stock (Detail) (USD $)	3 Months Ended
Mar. 31, 2012	Mar. 31, 2013 Restricted Stock
Number of Shares
Restricted stock at January 1, 2013		224,005
Granted		93,770
Vested		(70,133)
Restricted stock at March 31, 2013		247,642
Weighted Average Grant-Date Fair Value
Restricted stock at January 1, 2013		$ 17.40
Granted	$ 7.85	$ 20.26
Vested		$ 17.06
Restricted stock at March 31, 2013		$ 18.58

The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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