Investments in Marketable Securities (Detail) - Marketable securities - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 12,181	$ 19,552
Gross Unrealized Gain	1	2
Gross Unrealized Loss	(2)	(7)
Fair Value	12,180	19,547
U.S. Government and agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	402	807
Fair Value	402	807
Corporate and other debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	11,779	18,745
Gross Unrealized Gain	1	2
Gross Unrealized Loss	(2)	(7)
Fair Value	$ 11,778	$ 18,740