Schedule of Available for Sale Marketable Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	$ 469,504	$ 259,011
Available-for-sale marketable securities, Unrealized Gain	3,845	592
Available-for-sale marketable securities, Unrealized (Loss)	(438)	(2,967)
Available-for-sale marketable securities, Fair Market Value	472,911	256,636
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	38,277	191,978
U.S. Treasury Securities
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	189,927	110,969
Available-for-sale marketable securities, Unrealized Gain	668	112
Available-for-sale marketable securities, Unrealized (Loss)	(273)	(1,360)
Available-for-sale marketable securities, Fair Market Value	190,322	109,721
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	18,195	75,040
Commercial Paper
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	154,903	86,130
Available-for-sale marketable securities, Unrealized Gain	9	13
Available-for-sale marketable securities, Unrealized (Loss)	(2)	(26)
Available-for-sale marketable securities, Fair Market Value	154,910	86,117
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	10,322	85,094
Corporate Debt Securities
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	91,553	41,133
Available-for-sale marketable securities, Unrealized Gain	3,035	432
Available-for-sale marketable securities, Unrealized (Loss)	(157)	(1,545)
Available-for-sale marketable securities, Fair Market Value	94,431	40,020
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	4,581	24,767
Certificates of Deposit and Time Deposits
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	19,717	7,604
Available-for-sale marketable securities, Unrealized Gain	6
Available-for-sale marketable securities, Fair Market Value	19,723	7,604
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	2,232
U.S. Government Agency Securities
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	9,829	9,646
Available-for-sale marketable securities, Unrealized Gain	15	1
Available-for-sale marketable securities, Unrealized (Loss)	(6)	(36)
Available-for-sale marketable securities, Fair Market Value	9,838	9,611
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses	2,947	7,077
Debt Mutual Funds
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	3,187	3,153
Available-for-sale marketable securities, Unrealized Gain	112	34
Available-for-sale marketable securities, Fair Market Value	3,299	3,187
Non-U.S. Government Securities
Schedule of Available-for-sale Securities
Available-for-sale marketable securities, Cost	388	376
Available-for-sale marketable securities, Fair Market Value	$ 388	$ 376

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

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