Long-Term Investments - Additional Information (Detail) (USD $)	9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2011
Auction rate securities, par value	$ 7,241,000	$ 7,845,000
Minimum Period for which failed Auction Securities been in unrealized loss position	12 months
Fair value of Failed Auction Securities	6,231,000	6,736,000
Gross Unrealized Losses	1,018,000	1,121,000
Aggregate credit loss	395,000	317,000	292,000	308,000
Failed Auction Securities [Member]
Auction rate securities, par value	6,000,000	6,100,000
Interest rates auction time	28 days
Period for which Failed Auction Securities been in unrealized loss position	Exceeds 12 months
Fair value of Failed Auction Securities	4,982,000	4,979,000
Increase in fair value	103,000
Gross Unrealized Losses	1,018,000	1,121,000
Aggregate credit loss	395,000
Aggregate temporary impairment loss	623,000
Increased aggregate credit (losses) gains on Failed Auction Securities	$ 78,000