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Debt - Additional Information (Detail)
£ in Millions, CAD in Millions
1 Months Ended 2 Months Ended 3 Months Ended 12 Months Ended
Jan. 31, 2016
GBP (£)
Dec. 31, 2015
USD ($)
Jan. 31, 2016
GBP (£)
Nov. 01, 2015
USD ($)
Jul. 31, 2016
USD ($)
Jan. 31, 2016
CAD
Jan. 31, 2016
USD ($)
Debt Instrument [Line Items]              
Long-term debt       $ 7,300,000     $ 7,000,000
Current maturities       1,000,000     1,000,000
Line of Credit              
Debt Instrument [Line Items]              
Line of credit facility borrowing capacity £ 20.0   £ 20.0     CAD 30.0 150,000,000
Minimum funding threshold percent 40.00% 60.00%          
Commitment fee percentage 0.70% 0.65%          
Fair value of amount outstanding             148,700,000
Cash collateral of outstanding short-term borrowings   $ 20,000,000         35,000,000
Maximum borrowing capacity             250,000,000.0
Outstanding borrowing       $ 100,000,000     100,000,000
Weighted average interest rate during period     2.10% 1.80%      
Available borrowing capacity of facility             23,600,000
Line of Credit | LIBOR              
Debt Instrument [Line Items]              
Basis spread on variable rate 1.90% 1.75%          
Letter of Credit              
Debt Instrument [Line Items]              
Line of credit facility borrowing capacity             50,000,000
Fair value of amount outstanding             $ 25,100,000
Forecast | Line of Credit              
Debt Instrument [Line Items]              
Cash collateral of outstanding short-term borrowings         $ 50,000,000