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INVESTMENTS (Details) - USD ($)
$ in Thousands
12 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Mar. 31, 2016
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost $ 76,785 $ 7,059  
Gross Unrealized Gain 0 0  
Gross Unrealized (Loss) (236) (20)  
Fair Value 76,549 7,039  
Schedule of Held-to-maturity Securities [Line Items]      
Amortized Cost 63,197 66,693  
Gross Unrecognized Gain 1 1  
Gross Unrecognized (Loss) (347) (191)  
Fair Value 62,851 66,503  
Available-for-sale securities and Held-to-maturity securities [Abstract]      
Other-than-temporary impairment 0 0 $ 0
Unrealized loss on available-for-sale investments, net of related income taxes (200) (12)  
Redemptions of investments with callable provisions 900 0 $ 0
Available-for-sale investments by stated maturity, amortized cost [Abstract]      
Amortized Cost, Due in less than one year 70,625 6,381  
Amortized Cost, Due in 1 to 3 years 6,160 678  
Amortized Cost 76,785 7,059  
Available-for-sale investments by stated maturity, fair value [Abstract]      
Fair Value, Due in less than one year 70,429 6,377  
Fair Value, Due in 1 to 3 years 6,120 662  
Fair Value, Total investments 76,549 7,039  
Held-to-maturity investments by stated maturity, amortized cost [Abstract]      
Amortized Cost, Due in less than one year 50,077 45,184  
Amortized Cost, Due in 1 to 3 years 13,120 21,509  
Amortized Cost, Total investments 63,197 66,693  
Held-to-maturity investments by stated maturity, fair value [Abstract]      
Fair Value, Due in less than one year 49,902 45,124  
Fair Value, Due in 1 to 3 years 12,949 21,379  
Fair Value 62,851 66,503  
Unrealized loss position, fair value [Abstract]      
Less than 12 Months 116,323 51,135  
12 Months or greater 22,731 16,108  
Total 139,054 67,243  
Unrealized loss position, unrealized loss [Abstract]      
Less than 12 Months (426) (198)  
12 Months or greater (157) (13)  
Total (583) (211)  
Certificates of Deposit [Member]      
Unrealized loss position, fair value [Abstract]      
Less than 12 Months 8,899 2,738  
12 Months or greater 993 0  
Total 9,892 2,738  
Unrealized loss position, unrealized loss [Abstract]      
Less than 12 Months (19) (1)  
12 Months or greater (3) 0  
Total (22) (1)  
Commercial Paper [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 9,263    
Gross Unrealized Gain 0    
Gross Unrealized (Loss) (12)    
Fair Value 9,251    
Available-for-sale investments by stated maturity, amortized cost [Abstract]      
Amortized Cost 9,263    
Unrealized loss position, fair value [Abstract]      
Less than 12 Months 9,251 2,989  
12 Months or greater 0 0  
Total 9,251 2,989  
Unrealized loss position, unrealized loss [Abstract]      
Less than 12 Months (12) (3)  
12 Months or greater 0 0  
Total (12) (3)  
Corporate Bonds [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 66,868 6,381  
Gross Unrealized Gain 0 0  
Gross Unrealized (Loss) (220) (4)  
Fair Value 66,648 6,377  
Available-for-sale investments by stated maturity, amortized cost [Abstract]      
Amortized Cost 66,868 6,381  
Unrealized loss position, fair value [Abstract]      
Less than 12 Months 98,173 44,387  
12 Months or greater 21,088 16,108  
Total 119,261 60,495  
Unrealized loss position, unrealized loss [Abstract]      
Less than 12 Months (395) (177)  
12 Months or greater (150) (13)  
Total (545) (190)  
Municipal Bonds [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 654 678  
Gross Unrealized Gain 0 0  
Gross Unrealized (Loss) (4) (16)  
Fair Value 650 662  
Available-for-sale investments by stated maturity, amortized cost [Abstract]      
Amortized Cost 654 678  
Unrealized loss position, fair value [Abstract]      
Less than 12 Months 0 1,021  
12 Months or greater 650 0  
Total 650 1,021  
Unrealized loss position, unrealized loss [Abstract]      
Less than 12 Months 0 (17)  
12 Months or greater (4) 0  
Total (4) (17)  
Certificates of Deposit [Member]      
Schedule of Held-to-maturity Securities [Line Items]      
Amortized Cost 9,914 3,735  
Gross Unrecognized Gain 0 1  
Gross Unrecognized (Loss) (22) (1)  
Fair Value 9,892 3,735  
Held-to-maturity investments by stated maturity, fair value [Abstract]      
Fair Value 9,892 3,735  
Commercial Paper [Member]      
Schedule of Held-to-maturity Securities [Line Items]      
Amortized Cost   5,588  
Gross Unrecognized Gain   0  
Gross Unrecognized (Loss)   (3)  
Fair Value   5,585  
Held-to-maturity investments by stated maturity, fair value [Abstract]      
Fair Value   5,585  
Corporate Bonds [Member]      
Schedule of Held-to-maturity Securities [Line Items]      
Amortized Cost 52,938 57,009  
Gross Unrecognized Gain 0 0  
Gross Unrecognized (Loss) (325) (186)  
Fair Value 52,613 56,823  
Held-to-maturity investments by stated maturity, fair value [Abstract]      
Fair Value 52,613 56,823  
Municipal Bonds [Member]      
Schedule of Held-to-maturity Securities [Line Items]      
Amortized Cost 345 361  
Gross Unrecognized Gain 1 0  
Gross Unrecognized (Loss) 0 (1)  
Fair Value 346 360  
Held-to-maturity investments by stated maturity, fair value [Abstract]      
Fair Value $ 346 $ 360