Accounts Receivable Accounts Receivable (Allowance) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance at January 1	$ 2,357	$ 1,560	$ 1,259
Write-offs	(2,186)	(558)	(488)
Recoveries	2,587	236	139
Increase (decrease) in allowance	1,404	1,119	650
Balance at December 31	$ 4,162	$ 2,357	$ 1,560