Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands		12 Months Ended
		Apr. 25, 2020		Apr. 27, 2019	Apr. 28, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		$ 696,976		$ 625,216	$ 601,105
Cumulative effect adjustment for investments/Reclassification of certain income tax effects	[1]	0
Ending balance		716,306		696,976	625,216
Amount of pension termination charge reclassified from AOCI		0		23,807	0
Pension termination charge				28,200
Income tax expense				4,400
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning balance		696,976		625,216	601,105
Net income		78,984		70,141	81,595
Other comprehensive income (loss)		(3,209)		23,240	8,804
Change in noncontrolling interests		156
Ending balance		716,306		696,976	625,216
ASU 2016-01
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect adjustment for investments/Reclassification of certain income tax effects				0
Translation adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		50		2,388	(927)
Changes before reclassifications		(1,941)		(2,338)	3,315
Cumulative effect adjustment for investments/Reclassification of certain income tax effects		0		0
Amounts reclassified to net income		0		0	0
Tax effect		0		0	0
Total other comprehensive income		(1,941)		(2,338)	3,315
Ending balance		(1,891)		50	2,388
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning balance		50		2,388	(927)
Ending balance		(1,891)		50	2,388
Change in fair value of cash flow hedge
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		87		154	74
Changes before reclassifications		0		(369)	164
Cumulative effect adjustment for investments/Reclassification of certain income tax effects		(97)		0
Amounts reclassified to net income		14		280	(208)
Tax effect		(4)		22	124
Total other comprehensive income		(87)		(67)	80
Ending balance		0		87	154
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning balance		87		154	74
Ending balance		0		87	154
Unrealized gain (loss) on marketable securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		6		1,376	1,752
Changes before reclassifications		387		330	844
Cumulative effect adjustment for investments/Reclassification of certain income tax effects		258		(1,637)
Amounts reclassified to net income		(141)		25	(1,420)
Tax effect		(61)		(88)	200
Total other comprehensive income		443		(1,370)	(376)
Ending balance		449		6	1,376
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning balance		6		1,376	1,752
Ending balance		449		6	1,376
Unrealized gain (loss) on marketable securities | ASU 2016-01
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect adjustment for investments/Reclassification of certain income tax effects				1,600
Net pension amortization and net actuarial loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(3,605)		(29,117)	(33,782)
Changes before reclassifications		(1,809)		(479)	3,257
Cumulative effect adjustment for investments/Reclassification of certain income tax effects		(708)		0
Amounts reclassified to net income		218		26,553	3,341
Tax effect		394		(562)	(1,933)
Total other comprehensive income		(1,905)		25,512	4,665
Ending balance		(5,510)		(3,605)	(29,117)
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning balance		(3,605)		(29,117)	(33,782)
Ending balance		(5,510)		(3,605)	(29,117)
Accumulated other comprehensive loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(3,462)		(25,199)	(32,883)
Changes before reclassifications		(3,363)		(2,856)	7,580
Cumulative effect adjustment for investments/Reclassification of certain income tax effects		(547)	[1]	(1,637)
Amounts reclassified to net income		91		26,858	1,713
Tax effect		329		(628)	(1,609)
Total other comprehensive income		(3,490)		21,737	7,684
Ending balance		(6,952)		(3,462)	(25,199)
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning balance		(3,462)		(25,199)	(32,883)
Other comprehensive income (loss)		(2,943)		23,374	7,684
Ending balance		(6,952)		(3,462)	(25,199)
Accumulated other comprehensive loss | ASU 2016-01
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect adjustment for investments/Reclassification of certain income tax effects				(1,637)
Cumulative effect adjustment - unrealized gains on equity investments				2,100
Cumulative effect adjustment - tax expense				500
Non-Controlling Interests
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		14,468		13,035	11,186
Ending balance		15,553		14,468	13,035
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning balance		14,468		13,035	11,186
Net income		1,515		1,567	729
Other comprehensive income (loss)		(266)		(134)	1,120
Change in noncontrolling interests		(164)		0	0
Ending balance		$ 15,553		$ 14,468	$ 13,035

[1] Income tax effects of the Tax Cuts and Jobs Act are reclassified from Accumulated Other Comprehensive Income ("AOCI") to retained earnings due to the adoption of ASU 2018-02, Income Statement-Reporting Comprehensive Income (Topic 220).