Fair Value Measurements - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015	Mar. 18, 2013
Impaired Long Lived Assets Held And Used [Line Items]
Impairment of long-lived assets			$ 0		$ 0
Fair value of available for sale securities	$ 1,800,000		1,800,000		$ 3,900,000
Change in fair value of available for sale securities	$ 47,000	$ (948,000)	$ (2,179,000)	$ (650,000)
Convertible Notes | 1.50% Senior Subordinated Notes Due March 15, 2018
Impaired Long Lived Assets Held And Used [Line Items]
Debt instrument, interest rate, stated percentage	1.50%	1.50%	1.50%	1.50%	1.50%	1.50%