Short-Term and Long-Term Investments - Additional Information (Detail) (USD $)	9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Dec. 31, 2012
Unrealized Losses On Short Term And Long Term Investments [Line Items]
Amortized cost of securities	$ 6,710,000	$ 6,820,000
Minimum period for which failed auction securities been in unrealized loss position	12 months
Estimated fair value of securities	5,675,000	5,651,000
Gross unrealized losses	1,036,000	1,175,000
Aggregate credit loss	356,000	395,000	395,000	317,000
Failed Auction Securities [Member]
Unrealized Losses On Short Term And Long Term Investments [Line Items]
Amortized cost of securities	6,000,000	6,000,000
Period for which failed auction securities been in unrealized loss position	Exceeds 12 months
Estimated fair value of securities	4,964,000	4,825,000
Increase in fair value	139,000
Gross unrealized losses	1,036,000	1,175,000
Aggregate credit loss	356,000
Aggregate temporary impairment loss	$ 680,000