Marketable Investments - Additional Information (Detail) (USD $)				12 Months Ended		12 Months Ended	0 Months Ended	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2012 Accumulated Net Unrealized Investment Gain (Loss) [Member]	Dec. 31, 2013 ARS [Member]	Dec. 31, 2012 ARS [Member]	Dec. 31, 2012 ARS [Member] Level 3 [Member]	Oct. 30, 2013 ARS [Member] Subsequent Event [Member]	Dec. 31, 2013 Minimum [Member]	Dec. 31, 2012 Minimum [Member]	Dec. 31, 2013 Maximum [Member]	Dec. 31, 2012 Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Auction rate securities par value	$ 80,988,000	$ 145,512,000		$ 11,000,000	$ 11,000,000
Proceeds from sale of ARS							9,100,000
Loss realized on ARS				1,900,000			1,900,000
Intervals for each security								7 days		35 days
Interest rates on securities ranged								0.10%	0.10%	0.40%	0.50%
Weighted average interest rate						0.90%
Weighted average discount rate						3.90%
Weighted average holding period						8 years 8 months 12 days
Unrealized loss recorded in accumulated other comprehensive income			$ 2,000,000