CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares
Income Statement [Abstract]
Net sales	$ 812,021	$ 666,707	$ 1,974,437	$ 1,710,875
Cost of goods sold	533,631	418,015	1,271,127	1,083,908
Amortization of intangible assets and purchase accounting effect on inventory	2,789	1,929	6,304	4,705
Gross profit	275,601	246,763	697,006	622,262
Operating expenses:
Marketing and selling	116,153	102,036	325,917	279,700
Research and development	34,398	32,284	106,144	96,867
General and administrative	22,291	24,598	72,850	75,543
Amortization of intangible assets and acquisition-related costs	2,496	1,494	6,377	4,535
Change in fair value of contingent consideration for business acquisition	0	(9,925)	(4,908)	(9,925)
Total operating expenses	175,338	150,487	506,380	446,720
Operating income	100,263	96,276	190,626	175,542
Interest income	874	202	3,097	263
Other income (expense), net	(324)	2,634	(894)	943
Income before income taxes	100,813	99,112	192,829	176,748
Provision for income taxes	20,040	1,647	18,691	10,297
Net income	$ 80,773	$ 97,465	$ 174,138	$ 166,451
Net income per share:
Net income per share - basic (in dollars per share) | $ / shares	$ 0.49	$ 0.60	$ 1.06	$ 1.03
Net income per share - diluted (in dollars per share) | $ / shares	$ 0.48	$ 0.59	$ 1.03	$ 1.01
Weighted average shares used to compute net income per share:
Basic (in shares) | shares	164,248	161,977	163,924	162,070
Diluted (in shares) | shares	169,079	165,901	168,832	165,211
Cash dividend per share (in dollars per share) | (per share)	$ 0.00	$ 0.00	$ 0.63	$ 0.57