Debt - Additional Information (Details) - USD ($)	1 Months Ended				3 Months Ended		6 Months Ended
	Dec. 31, 2015	Sep. 30, 2014	Jul. 31, 2014	Aug. 31, 2013	Jul. 31, 2016	Jul. 31, 2015	Jul. 31, 2016	Jul. 31, 2015	Apr. 30, 2015	Mar. 31, 2015	Jan. 31, 2015
August Two Thousand Thirteen Facility | Letter of Credit
Debt Instrument [Line Items]
Line of credit facility, interest rate		3.25%
Line of credit facility, amount drawn		$ 25,000,000								$ 25,000,000
August Two Thousand Thirteen Facility | Secured Debt | Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		75,000,000		$ 100,000,000					$ 60,000,000
Line of credit facility, term				2 years
Line of credit facility, unused commitment fee percentage				0.50%
Line of credit facility, amount drawn			$ 12,000,000	$ 34,000,000
Line of credit facility, interest rate			3.30%	3.40%
Line of credit facility, amount paid down		$ 6,000,000
Line of credit facility maturity date		Aug. 31, 2016
Line of credit facility											$ 40,000,000
Line of credit facility, remaining borrowing capacity											$ 10,000,000
Repayments of outstanding principal balance	$ 40,000,000
Line of credit facility, interest expense					$ 200,000	$ 400,000	$ 400,000	$ 1,100,000
August Two Thousand Thirteen Facility | London Interbank Offer Rate (LIBOR) | Secured Debt | Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility, floating interest rate				3.00%
August Two Thousand Thirteen Facility | Alternate Base Rate (ABR) | Secured Debt | Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility, floating interest rate				2.00%
December Two Thousand Fifteen Facility | Secured Debt | Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	40,000,000
Line of credit facility, amount drawn	$ 40,000,000
Line of credit facility, interest rate	1.82%
Line of credit facility maturity date	Dec. 31, 2017
Debt instrument, description of variable rate basis							The December 2015 Facility is denominated in U.S. dollars and, depending on certain conditions, each borrowing is subject to a floating interest rate equal to either the prime rate plus a spread of 0.25% to 2.75% or a reserve adjusted LIBOR rate (based on one, three or six-month interest periods) plus a spread of 1.25% to 3.75%.
Line of credit facility, commitment fee percentage	0.20%
December Two Thousand Fifteen Facility | Secured Debt | Revolving Credit Facility | Minimum
Debt Instrument [Line Items]
Certificate of deposit held as collateral for letter of credit	$ 0
Minimum deposit amount with lender	$ 40,000,000
December Two Thousand Fifteen Facility | London Interbank Offer Rate (LIBOR) | Secured Debt | Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility, floating interest rate	1.25%
December Two Thousand Fifteen Facility | London Interbank Offer Rate (LIBOR) | Secured Debt | Revolving Credit Facility | Minimum
Debt Instrument [Line Items]
Line of credit facility, floating interest rate	1.25%
December Two Thousand Fifteen Facility | London Interbank Offer Rate (LIBOR) | Secured Debt | Revolving Credit Facility | Maximum
Debt Instrument [Line Items]
Line of credit facility, floating interest rate	3.75%
December Two Thousand Fifteen Facility | Prime Rate | Secured Debt | Revolving Credit Facility | Minimum
Debt Instrument [Line Items]
Line of credit facility, floating interest rate	0.25%
December Two Thousand Fifteen Facility | Prime Rate | Secured Debt | Revolving Credit Facility | Maximum
Debt Instrument [Line Items]
Line of credit facility, floating interest rate	2.75%