Available-for-Sale Marketable Securities in Unrealized Position (Detail) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value		$ 75,761,000
Less than 12 Months, Unrealized Loss		(253,000)
12 Months or Longer, Fair Value		10,975,000
12 Months or Longer, Unrealized Loss		(30,000)
Total, Fair Value		86,736,000
Total, Unrealized Loss	$ 0	(283,000)
United States government agency securities
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value		14,948,000
Less than 12 Months, Unrealized Loss		(22,000)
12 Months or Longer, Fair Value		999,000
12 Months or Longer, Unrealized Loss		(1,000)
Total, Fair Value		15,947,000
Total, Unrealized Loss		(23,000)
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value		60,813,000
Less than 12 Months, Unrealized Loss		(231,000)
12 Months or Longer, Fair Value		9,976,000
12 Months or Longer, Unrealized Loss		(29,000)
Total, Fair Value		70,789,000
Total, Unrealized Loss		$ (260,000)