Fair Value Measurements - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Mar. 18, 2013	May. 23, 2011
Impaired Long Lived Assets Held And Used [Line Items]
Impairment of long-lived assets	$ 0	$ 0
Fair value of available for sale securities	1,900,000	$ 3,900,000
Change in fair value of available for sale securities	$ (2,037,000)
Convertible Notes | 2.50% Senior Subordinated Notes Due June 2016
Impaired Long Lived Assets Held And Used [Line Items]
Debt instrument, interest rate, stated percentage	2.50%	2.50%	2.50%		2.50%
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%