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Long Term Debt - Additional Information (Detail) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Dec. 31, 2016
Mar. 17, 2014
Debt Instrument [Line Items]            
Letters of credit outstanding under the facility $ 12,300,000   $ 12,300,000   $ 13,000,000  
5.25% Senior Notes due March 15, 2019 [Member] | Senior Notes [Member]            
Debt Instrument [Line Items]            
Interest rate on Senior Notes 5.25%   5.25%     5.25%
Maturity date of Senior notes payable     Mar. 15, 2019      
Debt instrument interest rate term     Interest is payable semi-annually on March 15 and September 15 of each year.      
Debt instrument redemption date     On or after March 15, 2016      
Debt instrument restrictive covenants     The indenture governing the 2019 Notes (the “2019 Indenture”) contains, among other things, certain restrictive covenants, including limitations on incurring indebtedness, creating liens, selling assets and entering into certain transactions with affiliates. The covenants also limit PHI’s ability to, among other things, pay cash dividends on common stock, repurchase or redeem common or preferred equity, prepay subordinated debt and make certain investments.      
Percentage of principal amount redeemed     101.00%      
Interest Expense Fund [Member]            
Debt Instrument [Line Items]            
Periodic payment of debt interest $ 14,300,000 $ 13,900,000 $ 29,500,000 $ 28,300,000    
Revolving Credit Facility [Member]            
Debt Instrument [Line Items]            
Revolving credit facility, maturity date     Oct. 01, 2018      
Increased Borrowing capacity $ 150,000,000   $ 150,000,000      
Revolving Credit facility, Covenants, consolidated working capital ratio 200.00%   200.00%      
Revolving Credit facility, Covenants, consolidated net worth ratio 150.00%   150.00%      
Revolving Credit facility, Covenants, fixed coverage ratio 110.00%   110.00%      
Revolving Credit facility, Covenants, consolidated net worth $ 450,000,000   $ 450,000,000      
Letters of credit outstanding under the facility $ 7,800,000   $ 7,800,000      
Revolving Credit Facility [Member] | LIBOR [Member]            
Debt Instrument [Line Items]            
LIBOR plus interest rate on borrowed funds     2.25%