Marketable Securities - Marketable Securities Classified as Available-for-Sale (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 522	$ 51,007
Gross Unrealized Gain	0	140
Gross Unrealized Loss	0	(138)
Fair Value	522	51,009
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	522	25,608
Gross Unrealized Gain	0	122
Gross Unrealized Loss	0	(73)
Fair Value	$ 522	25,657
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		12,424
Gross Unrealized Gain		0
Gross Unrealized Loss		(31)
Fair Value		12,393
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		4,800
Gross Unrealized Gain		2
Gross Unrealized Loss		(23)
Fair Value		4,779
Government and agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		5,705
Gross Unrealized Gain		16
Gross Unrealized Loss		(9)
Fair Value		5,712
Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		2,470
Gross Unrealized Gain		0
Gross Unrealized Loss		(2)
Fair Value		$ 2,468