Investments - Unrealized Loss (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Apr. 01, 2018
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less Than 12 Months	$ 74,057	$ 118,225
Unrealized Loss, Less Than 12 Months	(1,014)	(1,635)
Fair Value, 12 Months or Greater	99,933	63,384
Unrealized Loss, 12 Months or Greater	(1,403)	(1,085)
Fair Value, Total	173,990	181,609
Unrealized Loss, Total	(2,417)	(2,720)
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less Than 12 Months	48,989	78,726
Unrealized Loss, Less Than 12 Months	(814)	(1,324)
Fair Value, 12 Months or Greater	51,168	23,286
Unrealized Loss, 12 Months or Greater	(690)	(380)
Fair Value, Total	100,157	102,012
Unrealized Loss, Total	(1,504)	(1,704)
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less Than 12 Months	9,546	14,147
Unrealized Loss, Less Than 12 Months	(45)	(90)
Fair Value, 12 Months or Greater	3,929	2,540
Unrealized Loss, 12 Months or Greater	(23)	(20)
Fair Value, Total	13,475	16,687
Unrealized Loss, Total	(68)	(110)
U.S. government treasuries and agencies securities
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less Than 12 Months	15,522	25,352
Unrealized Loss, Less Than 12 Months	(155)	(221)
Fair Value, 12 Months or Greater	44,836	34,920
Unrealized Loss, 12 Months or Greater	(690)	(673)
Fair Value, Total	60,358	60,272
Unrealized Loss, Total	$ (845)	(894)
International government bonds
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less Than 12 Months		0
Unrealized Loss, Less Than 12 Months		0
Fair Value, 12 Months or Greater		2,638
Unrealized Loss, 12 Months or Greater		(12)
Fair Value, Total		2,638
Unrealized Loss, Total		$ (12)