Stockholders' Equity (Details)					1 Months Ended			2 Months Ended	12 Months Ended
	Aug. 19, 2016 $ / shares	May 20, 2016 $ / shares	Feb. 17, 2016 $ / shares	Nov. 20, 2015 $ / shares	Jun. 30, 2016 USD ($) $ / shares shares	May 31, 2014 USD ($) $ / shares	May 31, 2009 USD ($)	May 31, 2014 USD ($) $ / shares shares	Jul. 31, 2016 USD ($) $ / shares shares	Jul. 31, 2015 USD ($) dividend $ / shares shares	Jul. 31, 2014 USD ($) $ / shares	Oct. 06, 2016 USD ($) $ / shares	Jun. 08, 2016 $ / shares	Mar. 10, 2016 $ / shares	Dec. 09, 2015 $ / shares	Sep. 28, 2015 $ / shares	Apr. 30, 2015 $ / shares	Jan. 31, 2015 $ / shares	Oct. 31, 2014 $ / shares
Class of Stock [Line Items]
Common stock issued in a public offering (in shares) | shares					7,145,000
Common stock price per share in a public offering (in dollars per share) | $ / shares					$ 14.00
Proceeds received from equity offering					$ 95,029,000				$ 95,029,000	$ 0	$ 0
Aggregate registered amount remained available for sale of securities, including debt, under the existing shelf registration statement									74,970,000
Total issuance costs related to common stock offering									1,112,000
Payments of issuance costs related to equity offering									476,000	$ 0	0
Adjustment to Additional Paid in Capital, Stock Issued, Issuance Costs									959,000
Stock Repurchase Program
Amount that remains to be expended under the current board repurchase authorization									8,664,000
Maximum amount authorized by the board of directors for the repurchase of shares of the company's common stock									$ 100,000,000
Shares acquired (in shares) | shares									0	175,735
Average price per share of shares repurchased on the open market (in dollars per share) | $ / shares										$ 28.39
Aggregate cost including transaction costs										$ 4,989,000	$ 70,729,000
Dividends
Targeted annual dividend per share (in dollars per share) | $ / shares									$ 1.20	$ 1.20	$ 1.10
Number of quarterly cash dividends declared during the period | dividend										4
Quarterly dividend paid amount per share (in dollars per share) | $ / shares		$ 0.300	$ 0.300	$ 0.300
3.0% Convertible Senior Notes
Debt Instrument, Face Amount							$ 200,000,000
Stated interest rate							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	$ 0	$ 50,037,000
Shares issued from the partial conversion of the 3.0% convertible senior notes (in shares) | shares								1,570,904
Debt Instrument, Convertible, Conversion Price (in dollars per share) | $ / 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
Repayment of 3.0% convertible senior notes						$ 149,963,000
Debt Instrument, Redemption Price, Percentage						100.00%
Amount of the 3.0% convertible senior notes outstanding at period end										$ 0
Dividend Declared - Subsequent [Member]
Class of Stock [Line Items]
Aggregate registered amount remained available for sale of securities, including debt, under the existing shelf registration statement												$ 74,970,000
Dividends
Quarterly dividend payment amount per share (in dollars per share) | $ / shares												$ 0.30
Quarterly dividend paid amount per share (in dollars per share) | $ / shares	$ 0.300
Dividend Declared - First [Member]
Dividends
Quarterly dividend payment amount per share (in dollars per share) | $ / shares																$ 0.30			$ 0.300
Dividend Declared Second [Member]
Dividends
Quarterly dividend payment amount per share (in dollars per share) | $ / shares															$ 0.30			$ 0.30
Dividend Declared - Third [Member]
Dividends
Quarterly dividend payment amount per share (in dollars per share) | $ / shares														$ 0.30			$ 0.30
Dividend Declared - Fourth [Member]
Dividends
Quarterly dividend payment amount per share (in dollars per share) | $ / shares										$ 0.30			$ 0.30