Short-Term and Long-Term Investments (Tables)

9 Months Ended

Jun. 30, 2020

Investments, Debt and Equity Securities [Abstract]

Schedule of Short-Term and Long-Term Investments

Short-term investments consist of the following (in thousands):

June 30, 2020	Cost or Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Corporate bonds and notes	$	202,968	$	900	$	(17)	$	203,851
Municipal bonds and notes	7,018		22		—		7,040
U.S. government securities	161,414		38		(35)		161,417
U.S. government agency securities	6,987		10		(2)		6,995
	$	378,387	$	970	$	(54)	$	379,303

September 30, 2019	Cost or Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Certificates of deposits	$	249	$	—	$	—	$	249
Corporate bonds and notes	259,242		402		(97)		259,547
Municipal bonds and notes	12,128		6		(5)		12,129
U.S. government securities	78,988		18		(14)		78,992
U.S. government agency securities	22,138		9		(1)		22,146
	$	372,745	$	435	$	(117)	$	373,063

Long-term investments consist of the following (in thousands):

June 30, 2020	Cost or Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Corporate bonds and notes	$	96,645	$	1,112	$	(80)	$	97,677
U.S. government securities	3,984		—		(2)		3,982
U.S. government agency securities	11,250		23		(4)		11,269
	$	111,879	$	1,135	$	(86)	$	112,928

September 30, 2019	Cost or Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Corporate bonds and notes	$	298,888	$	469	$	(441)	$	298,916
Municipal bonds and notes	2,528		2		(6)		2,524
U.S. government securities	5,515		3		(3)		5,515
U.S. government agency securities	51,463		5		(21)		51,447
	$	358,394	$	479	$	(471)	$	358,402

Schedule of Investments That Have Been in a Continuous Unrealized Loss Position

The following table summarizes investments that have been in a continuous unrealized loss position for less than 12 months and those that have been in a continuous unrealized loss position for more than 12 months as of June 30, 2020 (in thousands):

	Less Than 12 Months				12 Months or Greater				Total
June 30, 2020	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
Corporate bonds and notes	$	71,355	$	(92)	$	5,005	$	(5)	$	76,360	$	(97)
U.S. government securities	152,646		(37)		—		—		152,646		(37)
U.S. government agency securities	9,789		(6)		—		—		9,789		(6)
Total	$	233,790	$	(135)	$	5,005	$	(5)	$	238,795	$	(140)

The following table summarizes investments that have been in a continuous unrealized loss position for less than 12 months and those that have been in a continuous unrealized loss position for more than 12 months as of September 30, 2019 (in thousands):

	Less Than 12 Months				12 Months or Greater				Total
September 30, 2019	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
Corporate bonds and notes	$	237,747	$	(434)	$	109,613	$	(104)	$	347,360	$	(538)
Municipal bonds and notes	864		—		7,800		(11)		8,664		(11)
U.S. government securities	27,095		(12)		9,991		(5)		37,086		(17)
U.S. government agency securities	30,946		(22)		—		—		30,946		(22)
Total	$	296,652	$	(468)	$	127,404	$	(120)	$	424,056	$	(588)