Account Receivable (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable gross	$ 33,128	$ 23,327
Less allowance for doubtful accounts	(420)	(403)
Accounts receivable, net	32,708	22,924
Trade accounts receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable gross	17,428	14,965
Unpaid amounts for benefit services
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable gross	$ 15,700	$ 8,362