Amounts of Impairments Recorded and Presentation of Impairment Charges under Various Methods of Accounting (Parenthetical) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2010
Impairment Costs [Line Items]
Asset Impairment Charges, Total	$ 728,000	$ 2,914,000
GovDelivery
Impairment Costs [Line Items]
Asset Impairment Charges, Total	700,000
Gain on contingent consideration write-off	$ 700,000