Segment Reporting Segment Reporting (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Oct. 28, 2017 USD ($)	Oct. 29, 2016 USD ($)	Oct. 28, 2017 USD ($)	Oct. 29, 2016 USD ($)
Segment Reporting Information [Line Items]
Number of Reportable Segments			2
Deferred Compensation Arrangement with Individual, Compensation Expense			$ 5,000
Sales Revenue, Goods, Gross		$ 770,671		$ 1,009,908
Revenue, Net	$ 886,861	770,671	1,242,572	1,009,908
Gross Profit	216,558	171,514	281,271	218,927
Depreciation and amortization expense	16,704	12,987	31,721	25,908
Operating Income (Loss)	83,256	56,760	27,717	3,998
Interest Income (Expense), Net	(1,836)	(630)	(4,874)	(1,296)
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	81,420	56,130	22,843	2,702
BNC [Member]
Segment Reporting Information [Line Items]
Sales Revenue, Goods, Gross	761,787		1,011,764
Gross Profit	171,725		220,462
Depreciation and amortization expense	15,086		28,468
Operating Income (Loss)	55,062		(1,050)
MBS [Member]
Segment Reporting Information [Line Items]
Sales Revenue, Goods, Gross	134,851	0	274,652	0
Gross Profit	33,175	0	60,764	0
Depreciation and amortization expense	1,618	0	3,253	0
Operating Income (Loss)	16,536	0	28,722	0
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Sales Revenue, Goods, Gross	(9,777)	0	(43,844)	0
Gross Profit	11,658	0	45	0
Operating Income (Loss)	$ 11,658	$ 0	$ 45	$ 0