Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Movement in Valuation Allowances and Reserves [Roll Forward]
Provisions for doubtful accounts	$ 2,009	$ 1,304	$ 2,104
Allowance for Doubtful Accounts
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of year	5,200	5,500	5,700
Provisions for doubtful accounts	2,009	1,304	2,104
Deductions - returns and write-offs	1,509	1,604	2,304
Balance at end of year	$ 5,700	$ 5,200	$ 5,500