Cash Equivalents and Investments (Summary of Cash and Available-For-Sale Securities) (Detail) - USD ($) $ in Thousands	Mar. 31, 2020		Dec. 31, 2019
Schedule of Available-For-Sale Securities [Line Items]
Cash and cash equivalents	$ 125,512	[1]	$ 168,982	[2]
Cash [Member]
Schedule of Available-For-Sale Securities [Line Items]
Cash and cash equivalents	43,704		37,718
Money Market Funds [Member]
Schedule of Available-For-Sale Securities [Line Items]
Cash and cash equivalents	81,808		131,264
Discontinued Operations, Held-for-sale [Member]
Schedule of Available-For-Sale Securities [Line Items]
Cash and cash equivalents	$ 21,305		$ 24,469

[1] unaudited

[2] Note 1