Summary of Significant Accounting Policies - Allowance for Doubtful Accounts Receivable (Details 2) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Allowance for Doubtful Accounts Receivable
Balance, beginning of year	$ 2,359	$ 3,147	$ 2,421
Additions (reductions) to expense	1,406	(354)	1,039
Write-offs	(465)	(280)	(174)
Other	23	(154)	(139)
Balance, end of year	$ 3,323	$ 2,359	$ 3,147