Description of Business and Summary of Significant Accounting Policies - Changes in Allowance for Doubtful Accounts for Trade Accounts Receivable (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 beginning of year	$ 418	$ 762	$ 924
Bad debt expense	2,456	1,640	1,678
Losses charged to allowance	(2,743)	(2,586)	(2,218)
Recoveries added to allowance	628	602	378
Balance at end of year	$ 759	$ 418	$ 762