Investments in Marketable Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 19,552	$ 19,326
Gross Unrealized Gain		7
Gross Unrealized Loss		(18)
Fair Value	19,547	19,315
Marketable securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	19,552	17,688
Gross Unrealized Gain	2	7
Gross Unrealized Loss	(7)	(13)
Fair Value	19,547	17,682
Marketable securities | U.S. Government and agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	807	7,029
Gross Unrealized Loss		(6)
Fair Value	807	7,023
Marketable securities | Corporate and other debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	18,745	10,659
Gross Unrealized Gain	2	7
Gross Unrealized Loss	(7)	(7)
Fair Value	$ 18,740	10,659
Long-term marketable securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		1,638
Gross Unrealized Loss		(5)
Fair Value		1,633
Long-term marketable securities | U.S. Government and agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		838
Gross Unrealized Loss		(2)
Fair Value		836
Long-term marketable securities | Corporate and other debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		800
Gross Unrealized Loss		(3)
Fair Value		$ 797