Available-for-Sale Marketable Securities in Unrealized Position (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 40,121	$ 20,170
Less than 12 Months, Unrealized Loss	(24)	(46)
12 Months or Longer, Fair Value		5,528
12 Months or Longer, Unrealized Loss		(3)
Total, Fair Value	40,121	25,698
Total, Unrealized Loss	(24)	(49)
United States government agency securities
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	6,035
Less than 12 Months, Unrealized Loss	(1)
Total, Fair Value	6,035
Total, Unrealized Loss	(1)
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	34,086	20,170
Less than 12 Months, Unrealized Loss	(23)	(46)
12 Months or Longer, Fair Value		5,528
12 Months or Longer, Unrealized Loss		(3)
Total, Fair Value	34,086	25,698
Total, Unrealized Loss	$ (23)	$ (49)