XML 42 R30.htm IDEA: XBRL DOCUMENT v3.8.0.1
Debt - Additional Information (Detail) - USD ($)
1 Months Ended 3 Months Ended
Jan. 20, 2016
Apr. 30, 2018
Mar. 31, 2018
Debt Instrument [Line Items]      
Agreement date     Apr. 18, 2014
Minimum asset coverage ratio 150.00%    
Maximum capitalization ratio 45.00%   50.00%
Base rate 0.75%    
Percentage increase in commitment fee 0.05%    
Percentage of equity in customary security interest 65.00%    
Senior secured revolving credit facility commitment     $ 750,000,000
Line of Credit Facility, Expiration Date     Apr. 18, 2019
Minimum [Member]      
Debt Instrument [Line Items]      
Line of credit covenant trigger percentage     25.00%
Standby Letters of Credit [Member]      
Debt Instrument [Line Items]      
Line of credit facility borrowings $ 40,000,000    
Swing Line Loan [Member]      
Debt Instrument [Line Items]      
Line of credit facility borrowings $ 25,000,000    
Senior Secured Revolving Credit Facility [Member]      
Debt Instrument [Line Items]      
Line of credit facility borrowings     $ 175,000,000
Line of Credit Facility, Available Borrowing Capacity     $ 452,000,000
Line Of credit Unused Capacity Percentage     71.00%
Letters of credit     $ 6,000,000
Casualty insurance, expiration month and year     2018-07
Senior Secured Revolving Credit Facility [Member] | Subsequent Event [Member]      
Debt Instrument [Line Items]      
Line of Credit Facility, Available Borrowing Capacity   $ 1,000,000,000  
Line of credit facility, maturity period   2023-04  
Accordion Debt [Member]      
Debt Instrument [Line Items]      
Senior secured revolving credit facility commitment     $ 250,000,000