Summary Selected Quarterly Financial Data - Additional Information (Detail) (USD $)	3 Months Ended							12 Months Ended			3 Months Ended				12 Months Ended	3 Months Ended				12 Months Ended		3 Months Ended	12 Months Ended
	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Income Tax Expense [Member]	Jun. 30, 2013 Income Tax Expense [Member]	Dec. 31, 2012 Income Tax Expense [Member]	Sep. 30, 2012 Income Tax Expense [Member]	Dec. 31, 2012 Income Tax Expense [Member]	Jun. 30, 2013 Adjustments Related to Insignificant Variances in Deferred Revenue [Member]	Mar. 31, 2013 Adjustments Related to Insignificant Variances in Deferred Revenue [Member]	Dec. 31, 2012 Adjustments Related to Insignificant Variances in Deferred Revenue [Member]	Sep. 30, 2012 Adjustments Related to Insignificant Variances in Deferred Revenue [Member]	Dec. 31, 2012 Adjustments Related to Insignificant Variances in Deferred Revenue [Member]	Dec. 31, 2011 Adjustments Related to Insignificant Variances in Deferred Revenue [Member]	Sep. 30, 2013 Income Tax Benefit Expense [Member]	Dec. 31, 2013 ARS [Member]
Effect of Fourth Quarter Events [Line Items]
Loss for sale of portfolio of auction rate securities																							$ 1,900,000
Deferred income tax benefit					5,900,000
Adjustments related to prior period											100,000	800,000	100,000	400,000	400,000					100,000	(400,000)	100,000
Increase (decrease) to revenue			(100,000)		100,000		(100,000)									(200,000)	(100,000)	100,000	200,000
Gain (losses) on investments	600,000	100,000	(100,000)	(100,000)				(2,433,000)	94,000	(399,000)
Increase (decrease) in general and administrative expense				$ (500,000)	$ 300,000	$ 200,000