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		$ 5,215,000	$ 6,990,000	$ 7,446,000
Charged to Costs & Expenses		90,000	270,000	129,000
Charged to Other Accounts	[1]	146,000	(2,037,000)	(565,000)
Deductions	[2]	(40,000)	(8,000)	(20,000)
Balance at End of Year		5,411,000	5,215,000	6,990,000
Deferred tax valuation allowance [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year		108,000	108,000	108,000
Charged to Costs & Expenses		348,000	0	0
Balance at End of Year		$ 456,000	$ 108,000	$ 108,000

[1] Expected customer account adjustments charged to revenue and write-offs, net of recoveries

[2] Represents bad debt recoveries