Schedule II - Consolidated Valuation and Qualifying Accounts (Details 2) - Allowance for doubtful accounts [Member] - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for doubtful accounts:
Balance, beginning of period		$ 10,479	$ 9,835	$ 9,511
Charged to costs and expenses		7,024	8,302	11,343
Other	[1]	989	851	1,012
Deductions	[2]	10,423	8,509	12,031
Balance, end of period		$ 8,069	$ 10,479	$ 9,835

[1] Recoveries.

[2] Uncollectible accounts written off.