OTHER CURRENT AND NONCURRENT ASSETS: (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Mar. 31, 2019
Other current assets
Prepaid expenses and other	$ 17,318	$ 9,058
Post-closing receivable from IPG	17,625	17,625
Interest receivable	1,366	2,497
Assets of non-qualified retirement plan	14,746	14,970
Other current assets	51,055	44,150
Other noncurrent assets
Acquired intangible assets, net	30,873	24,217
Right of use asset	19,158	0
Other miscellaneous noncurrent assets	8,626	8,282
Other assets, net	$ 58,657	$ 32,499