Goodwill and other intangible assets - Information Regarding Company's Goodwill and Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2018
Schedule Of Intangible Assets And Goodwill [Line Items]
Finite-lived intangibles, Gross carrying amount	$ 85,040	$ 72,700	$ 72,700
Finite-lived intangibles, Accumulated amortization	(46,430)	(39,447)	(37,727)
Finite-lived intangibles, Net carrying amount	38,610	33,253	34,973
Goodwill, Gross carrying amount	171,321	157,264	157,264
Goodwill, Accumulated amortization	0	0	0
Goodwill, Net carrying amount	171,321	157,264	157,264
Goodwill and other intangibles, Gross carrying amount	320,161	293,764	293,764
Goodwill and other intangibles, Accumulated amortization	(46,430)	(39,447)	(37,727)
Goodwill and other intangibles, Net carrying amount	273,731	254,317	256,037
Trademarks
Schedule Of Intangible Assets And Goodwill [Line Items]
Indefinite-lived intangibles, gross carrying amount	63,800		63,800
Indefinite-lived intangibles, accumulated amortization	0
Indefinite lived intangibles, Net carrying amount	63,800	63,800	63,800
Customer relationships – retailers
Schedule Of Intangible Assets And Goodwill [Line Items]
Finite-lived intangibles, Gross carrying amount	77,600	68,800	68,800
Finite-lived intangibles, Accumulated amortization	(42,500)	(35,547)	(33,827)
Finite-lived intangibles, Net carrying amount	$ 35,100	$ 33,253	$ 34,973
Finite-lived intangibles, estimated useful life	10 years	10 years	10 years
Customer relationships – e-commerce
Schedule Of Intangible Assets And Goodwill [Line Items]
Finite-lived intangibles, Gross carrying amount	$ 3,940	$ 3,900	$ 3,900
Finite-lived intangibles, Accumulated amortization	(3,901)	(3,900)	(3,900)
Finite-lived intangibles, Net carrying amount	$ 39	$ 0	$ 0
Finite-lived intangibles, estimated useful life	3 years	3 years	3 years
Trademarks
Schedule Of Intangible Assets And Goodwill [Line Items]
Finite-lived intangibles, Gross carrying amount	$ 3,500
Finite-lived intangibles, Accumulated amortization	(29)
Finite-lived intangibles, Net carrying amount	$ 3,471
Finite-lived intangibles, estimated useful life	10 years