Allowance for Doubtful Accounts Roll Forward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Allowance for doubtful accounts
Balance, beginning of year	$ 1,417	$ 1,844	$ 3,686
Provision (net of recovery)	898	346	(306)
Amounts written off, net of recoveries	(486)	(773)	(1,536)
Balance, end of year	$ 1,829	$ 1,417	$ 1,844