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Valuation and Qualifying Accounts (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Allowance for Uncollectible Trade Accounts [Member]      
Valuation and Qualifying Accounts Disclosure [Line Items]      
Balance at Beginning of Year $ 6,990,000 $ 7,446,000 $ 6,689,000
Charged to Costs & Expenses 270,000 129,000 662,000
Charged to Other Accounts [1] (2,037,000) (565,000) 142,000
Deductions [2] (8,000) (20,000) (47,000)
Balance at End of Year 5,215,000 6,990,000 7,446,000
Deferred tax valuation allowance [Member]      
Valuation and Qualifying Accounts Disclosure [Line Items]      
Balance at Beginning of Year 108,000 108,000 122,000
Charged to Costs & Expenses 0 0 (14,000)
Balance at End of Year $ 108,000 $ 108,000 $ 108,000
[1] Expected customer account adjustments charged to revenue and write-offs, net of recoveries
[2] Represents bad debt recoveries