Equity Compensation Plans Stock Options (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2013
Shares
Outstanding at March 31, 2013	772
Exercisable at March 31, 2013	463
Expected to vest at March 31, 2013	295
Weighted-Average Exercise Price
Outstanding at March 31, 2013	$ 9.63
Exercisable at March 31, 2013	$ 9.11
Expected to vest at March 31, 2013	$ 10.39
Weighted- Average Remaining Contractual Term (years)
Outstanding at March 31, 2013	6 years 1 month 6 days
Exercisable at March 31, 2013	4 years 4 months 24 days
Expected to vest at March 31, 2013	8 years 9 months 18 days
Aggregate Intrinsic Value
Outstanding at March 31, 2013	$ 4,454
Exercisable at March 31, 2013	2,925
Expected to vest at March 31, 2013	$ 1,464

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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