Investments in Marketable Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 22,431	$ 26,643
Gross Unrealized Gain	11	6
Gross Unrealized Loss	(1)	(9)
Fair Value	22,441	26,640
Marketable securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	20,782	23,089
Gross Unrealized Gain	9	6
Gross Unrealized Loss	(1)	(5)
Fair Value	20,790	23,090
Marketable securities | U.S. Government and agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	11,053	12,716
Gross Unrealized Gain	4	2
Gross Unrealized Loss		(2)
Fair Value	11,057	12,716
Marketable securities | Corporate and other debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	9,729	10,373
Gross Unrealized Gain	5	4
Gross Unrealized Loss	(1)	(3)
Fair Value	9,733	10,374
Long-term marketable securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,649	3,554
Gross Unrealized Gain	2
Gross Unrealized Loss		(4)
Fair Value	1,651	3,550
Long-term marketable securities | U.S. Government and agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,649	1,228
Gross Unrealized Gain	2
Fair Value	$ 1,651	1,228
Long-term marketable securities | Corporate and other debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		2,326
Gross Unrealized Loss		(4)
Fair Value		$ 2,322