Schedule V - Valuation and Qualifying Accounts (Details) - Allowance for doubtful accounts - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Movement in valuation and qualifying accounts
Balance at Beginning of Period	$ 425	$ 462	$ 456
Charged to Costs and Expenses	1,162	1,008	1,131
Deductions	1,152	1,045	1,125
Balance at End of Period	$ 435	$ 425	$ 462