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Schedule II - Valuation and Qualifying Accounts (Detail) - USD ($)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Valuation and Qualifying Accounts [Abstract]      
Balance at beginning of year $ 1,129,301 $ 848,767 $ 712,285
Amount charged against operating revenue 7,464,030 6,389,195 5,403,437
Accounts receivable contractual adjustments and write-offs (net of recoveries) (7,368,965) (6,108,661) (5,266,955)
Balance at end of year $ 1,224,366 $ 1,129,301 $ 848,767