Long-Term Investments - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Unrealized Losses On Short Term And Long Term Investments [Line Items]
Amortized cost of securities		$ 3,340,000
Minimum period for which failed auction securities been in unrealized loss position	12 months
Estimated Fair Value		2,866,000
Gross unrealized losses		474,000
Aggregate credit loss	$ 59,000	72,000	$ 84,000	$ 395,000
Failed Auction Security [Member]
Unrealized Losses On Short Term And Long Term Investments [Line Items]
Amortized cost of securities	$ 3,000,000	3,000,000
Period for which failed auction securities been in unrealized loss position	Exceeds 12 months
Estimated Fair Value	$ 2,508,000	2,526,000
Gross unrealized losses	492,000	$ 474,000
Aggregate credit loss	59,000
Aggregate temporary impairment loss	$ 433,000