Stock-Based Compensation, Stock Options (Details) (USD $)	12 Months Ended
	Apr. 25, 2015	Apr. 26, 2014	Apr. 27, 2013
Stock-Based Compensation
Expense recognized	$ 11,377,000	$ 14,475,000	$ 13,628,000
Cash received for exercises of stock options	1,397,000	3,565,000	2,901,000
Stock Options
Stock-Based Compensation
Cash received for exercises of stock options	1,400,000	3,600,000	2,900,000
Number of Shares
Outstanding, at beginning of period (in shares)	798,000
Granted (in shares)	373,711
Exercised (in shares)	(130,000)
Outstanding, at end of period (in shares)	1,042,000	798,000
Exercisable (in shares)	382,000
Weighted Average Exercise Price
Outstanding, at beginning of period (in dollars per share)	$ 11.79
Granted (in dollars per share)	$ 23.63
Exercised (in dollars per share)	$ 10.71
Outstanding, at end of period (in dollars per share)	$ 16.15	$ 11.79
Exercisable (in dollars per share)	$ 10.78
Additional information
Weighted Average Remaining Contractual Term, Outstanding	7 years 7 months 6 days	7 years 6 months
Weighted Average Remaining Contractual Term, Exercisable	6 years 4 months 24 days
Aggregate Intrinsic Value, Outstanding	11,773,000	10,185,000
Aggregate Intrinsic Value, Exercised	2,011,000	8,300,000	6,000,000
Aggregate Intrinsic Value, Exercisable	6,387,000
Unrecognized compensation cost	1,800,000
Period for recognition of unrecognized compensation costs	1 year 9 months 18 days
Vested during the period (in shares)	200,000
Fair value assumptions
Risk-free interest rate (as a percent)	1.59%	0.84%	0.75%
Dividend rate (as a percent)	1.00%	0.84%	0.00%
Expected life in years	5 years	5 years	5 years
Stock price volatility (as a percent)	54.40%	81.30%	83.80%
Fair value per share (in dollars per share)	$ 10.45	$ 11.63	$ 7.87
Stock Options | Minimum
Stock-Based Compensation
Purchase price of common stock at date of grant (as a percent)	1.00%
Vesting period	1 year
Stock Options | Maximum
Stock-Based Compensation
Vesting period	4 years
Stock Options | Selling, General and Administrative Expense
Stock-Based Compensation
Expense recognized	$ 3,000,000	$ 2,100,000	$ 2,300,000
Stock Options | Former Long-Term Equity Award Plan | Minimum
Stock-Based Compensation
Award expiration term	5 years
Stock Options | Former Long-Term Equity Award Plan | Maximum
Stock-Based Compensation
Award expiration term	10 years