OTHER CURRENT AND NONCURRENT ASSETS: (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Mar. 31, 2019
Other current assets
Prepaid expenses and other	$ 12,628	$ 9,058
Post-closing receivable from IPG	17,625	17,625
Interest receivable	1,080	2,497
Assets of non-qualified retirement plan	14,886	14,970
Other current assets	46,219	44,150
Other noncurrent assets
Acquired intangible assets, net	27,702	24,217
Right of use asset	17,947	0
Other miscellaneous noncurrent assets	8,591	8,282
Other assets, net	$ 54,240	$ 32,499