Stockholders' Equity (Details)	1 Months Ended		2 Months Ended	12 Months Ended
	May. 31, 2014 USD ($) $ / shares	May. 31, 2009 USD ($)	May. 31, 2014 USD ($) $ / shares shares	Jul. 31, 2015 USD ($) $ / shares shares	Jul. 31, 2014 USD ($) dividend $ / shares shares	Jul. 31, 2013 USD ($) $ / shares	Sep. 28, 2015 $ / shares	Sep. 25, 2015 USD ($)	Jun. 04, 2015 $ / shares	Mar. 11, 2015 $ / shares	Oct. 09, 2014 $ / shares	Jun. 05, 2014 $ / shares	Mar. 06, 2014 $ / shares	Dec. 09, 2013 $ / shares	Oct. 03, 2013 $ / shares
Stock Repurchase Program
Maximum amount authorized by the board of directors for the repurchase of shares of the company's common stock				$ 100,000,000
Shares acquired | shares				175,735	2,249,081
Average price per share of shares repurchased on the open market | $ / shares				$ 28.39	$ 31.45
Aggregate cost including transaction costs				$ 4,989,000	$ 70,729,000	$ 26,954,000
Amount that remains to be expended under the current board repurchase authorization				$ 8,664,000
Dividends
Targeted annual dividend per share | $ / shares				$ 1.20	$ 1.20	$ 1.10
Number of quarterly cash dividends declared during the period | dividend					4
3.0% Convertible Senior Notes
Debt Instrument, Face Amount		$ 200,000,000
Debt Instrument, Interest Rate, Stated Percentage		3.00%
Proceeds from Debt, Net of Issuance Costs		$ 194,541,000
Amount Of Initial Purchasers' Discount And Other Transaction Costs Related To Debt Issuance		5,459,000
Principal amount of 3.0% convertible senior notes converted into common stock			$ 50,037,000	$ 0	$ 50,037,000	$ 0
Shares issued from the partial conversion of the 3.0% convertible senior notes (in shares) | shares			1,570,904
Debt Instrument, Convertible, Conversion Price | $ / shares	$ 31.85		$ 31.85
Debt Instrument, Convertible, Conversion Ratio			31.3953
Original principal amount of each 3.0% convertible senior note		$ 1,000
Net increase to additional paid-in capital as a result of the partial conversion of the 3.0% convertible senior notes			$ 49,596,000
Amount of the 3.0% convertible senior notes redeemed or repurchased for cash	$ 149,963,000			$ 0	149,963,000	$ 0
Debt Instrument, Redemption Price, Percentage	100.00%
Amount of the 3.0% convertible senior notes outstanding at period end					$ 0
Remaining Authorization - Subsequent [Member]
Stock Repurchase Program
Amount that remains to be expended under the current board repurchase authorization								$ 8,664,000
Dividend Declared - Subsequent [Member]
Dividends
Quarterly dividend payment amount per share | $ / shares							$ 0.30
Dividend Declared - First [Member]
Dividends
Quarterly dividend payment amount per share | $ / shares											$ 0.30				$ 0.275
Dividend Declared Second [Member]
Dividends
Quarterly dividend payment amount per share | $ / shares											$ 0.30			$ 0.30
Dividend Declared - Third [Member]
Dividends
Quarterly dividend payment amount per share | $ / shares										$ 0.30			$ 0.30
Dividend Declared - Fourth [Member]
Dividends
Quarterly dividend payment amount per share | $ / shares									$ 0.30			$ 0.30