Debt - Additional Information (Details) - USD ($)			1 Months Ended		12 Months Ended
	Nov. 29, 2017	Nov. 27, 2017	Feb. 28, 2017	Dec. 31, 2015	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Debt Instrument [Line Items]
Decrease in restricted cash	$ 26,100,000
Interest cost capitalized					$ 29,000	$ 27,000	$ 400,000
Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility, interest expense					1,000,000	900,000	1,900,000
Interest cost capitalized					$ 29,000	$ 27,000	$ 400,000
December 2015 Facility | Revolving Credit Facility | Secured Debt
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity				$ 40,000,000
Line of credit facility maturity date			Dec. 31, 2018	Dec. 31, 2017
Line of credit facility, floating interest rate				1.25%
Debt instrument, description of variable rate basis					The December 2015 Facility was denominated in U.S. dollars and, depending on certain conditions, each borrowing was 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%
Line of credit facility, amount drawn				$ 40,000,000
Line of credit facility, interest rate				1.82%
Repayment of outstanding principal balance		$ 40,000,000
Line of credit facility, termination date		Nov. 27, 2017
December 2015 Facility | Revolving Credit Facility | Secured Debt | Minimum
Debt Instrument [Line Items]
Minimum deposit held as collateral for line of credit				$ 0
Minimum deposit amount with lender				$ 40,000,000
December 2015 Facility | Revolving Credit Facility | Secured Debt | Minimum | Prime Rate
Debt Instrument [Line Items]
Line of credit facility, floating interest rate				0.25%
December 2015 Facility | Revolving Credit Facility | Secured Debt | Minimum | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Line of credit facility, floating interest rate				1.25%
December 2015 Facility | Revolving Credit Facility | Secured Debt | Maximum | Prime Rate
Debt Instrument [Line Items]
Line of credit facility, floating interest rate				2.75%
December 2015 Facility | Revolving Credit Facility | Secured Debt | Maximum | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Line of credit facility, floating interest rate				3.75%
November 2017 Facility | Secured Debt | Wells Fargo Bank
Debt Instrument [Line Items]
Line of credit facility maturity date		Nov. 27, 2020
November 2017 Facility | Revolving Credit Facility | Secured Debt | Wells Fargo Bank
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		$ 85,000,000
Line of credit facility, interest payment terms					Interest on the revolving loans is payable quarterly in arrears with respect to loans based on the prime rate and at the end of an interest period in the case of loans based on the LIBOR rate (or at each three-month interval if the interest period is longer than three months).
November 2017 Facility | Revolving Credit Facility | Secured Debt | Prime Rate | Wells Fargo Bank
Debt Instrument [Line Items]
Line of credit facility, floating interest rate		0.25%
November 2017 Facility | Revolving Credit Facility | Secured Debt | London Interbank Offered Rate (LIBOR) | Wells Fargo Bank
Debt Instrument [Line Items]
Line of credit facility, floating interest rate		1.00%
November 2017 Facility | Letter of Credit | Secured Debt | Wells Fargo Bank
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity sublimit		$ 30,000,000