Acquisition of Ignis ASA (Details) Share data in Millions, except Per Share data, unless otherwise specified	6 Months Ended				0 Months Ended	1 Months Ended		2 Months Ended		3 Months Ended					3 Months Ended
	Oct. 30, 2011 USD ($)	Oct. 31, 2010 USD ($)	Jul. 31, 2011 USD ($)	Apr. 30, 2011 USD ($)	Jun. 29, 2011 Ignis ASA [Member] NOK	Jun. 22, 2011 Ignis ASA [Member] NOK	May 18, 2011 Ignis ASA [Member]	May 18, 2011 Ignis ASA [Member] USD ($)	May 18, 2011 Ignis ASA [Member] NOK	Oct. 30, 2011 Ignis ASA [Member] USD ($)	May 17, 2011 Ignis ASA [Member] USD ($)	Oct. 30, 2011 Ignis ASA [Member] In Process Research And Development [Member] USD ($)	Oct. 30, 2011 Ignis ASA [Member] Minimum [Member]	Oct. 30, 2011 Fi-ra Photonics [Member] USD ($)	Oct. 30, 2011 Purchased Technology [Member] Ignis ASA [Member] USD ($)	Oct. 30, 2011 Purchased Customer Relationships [Member] Ignis ASA [Member] USD ($)	Oct. 30, 2011 Internal Use Software [Member] Ignis ASA [Member] USD ($)	Oct. 30, 2011 Trade Names [Member] Ignis ASA [Member] USD ($)	Oct. 30, 2011 Order Backlog [Member] Ignis ASA [Member] USD ($)
Business Acquisition, Cost of Acquired Entity [Abstract]
Acquisition price per share					8	8			8
Business acquisition number of shares Acquired						12.8	38.1
Step acquisition, equity interest in acquiree shares											25.7
Payments to acquire business								$ 54,700,000
Percentage of voting interests acquired						97.00%	81.00%	81.00%	81.00%
Ownership percent triggering right to effect compulsory acquisition of Ignis ASA						90.00%
Cumulative percentage ownership after all transactions					100.00%
Number of subsidiaries operated by Ignis										4
Subsidiary ownership percentage														71.80%
Equity method ownership percent prior to acquisition											32.00%
Fair value of equity method ownership interest at acquisition date											36,600,000
Gain on fair value remeasurement of equity investment	5,429,000	0
Fair Value of Consideration Transferred and Contingent Consideration Details [Abstract]
Cash			98,900,000
Contingent consideration	14,340,000		13,598,000
Total			112,498,000
Contingent Consideration, potential cash payment										14,300,000
Discount rate for estimating fair value, using income approach													5.50%
Probability (in percent) of meeting milestones established for contingent consideration										100.00%
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]
Cash and cash equivalents										5,543,000
Accounts receivable										11,267,000
Inventory										14,721,000
Other current assets										2,161,000
Property, equipment and improvements										6,515,000
Intangible assets										34,860,000
Other assets										1,457,000
Total identifiable assets acquired										76,524,000
Current liabilities										(17,439,000)
Short-term debt										(9,985,000)
Long-term debt										(7,526,000)
Deferred tax liabilities										(3,553,000)
Other long-term liabilities										(330,000)
Total liabilities assumed										(38,833,000)
Net identifiable assets acquired										37,691,000
Non-controlling interest										(8,300,000)				(8,300,000)
Goodwill	82,936,000		83,107,000	0						83,107,000
Net assets acquired										112,498,000
Acquired Intangible Assets [Abstract]
Acquired indefinite-lived intangible asset, amount												250,000
Acquired finite-lived intangible asset, amount										34,600,000					16,300,000	16,300,000	880,000	800,000	350,000
Acquired finite-lived intangible asset, life										9					7	12	7	15	1
Non-controlling interest in subsidiary of acquired entity														28.20%
Gross contractual amount of accounts receivable acquired										11,600,000
Estimated uncollectible amount of receivables in acquisition										300,000
Acquisition related costs expensed										$ 1,100,000