Summary of Significant Accounting Policies - Allowance for Doubtful Accounts Receivable (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Allowance for Doubtful Accounts Receivable
Balance, beginning of year	$ 3,600	$ 3,323	$ 2,359
Additions to expense	614	533	1,406
Write-offs	(1,102)	(318)	(465)
Recoveries		89
Other	(32)	(27)	23
Balance, end of year	$ 3,080	$ 3,600	$ 3,323