Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2016

Schedule of black-scholes option-pricing model assumptions

The following information represents the weighted average of the assumptions used in the Black-Scholes option-pricing model for the ESPP:



	For the Years Ended December 31,
	2016		2015		2014
Risk-free interest rate	0.6	%	0.3	%	n/a
Expected term (in years)	0.5		0.5		n/a
Estimated dividend yield	—	%	—	%	n/a
Estimated volatility	37.6	%	33.5	%	n/a

The following information represents the weighted average of the assumptions used in the Black-Scholes option-pricing model for stock options granted during each of the last three years:



	For the Years Ended December 31,
	2016		2015		2014
Risk-free interest rate	1.4	%	1.8	%	1.9	%
Expected term (in years)	5.8		6.0		6.0
Estimated dividend yield	—	%	—	%	—	%
Estimated volatility	48.8	%	41.8	%	49.9	%

Reconciliation of beginning and ending amount of allowance for doubtful accounts

A reconciliation of the beginning and ending amount of allowance for doubtful accounts for the years ended December 31, 2016, 2015 and 2014, is as follows (in thousands):



	2016			2015			2014
Beginning balance, January 1	$	2,578		$	2,177		$	1,021
Additions and adjustments	3,165			1,368			2,084
Write-offs	(2,211		)	(967		)	(928		)
Ending balance, December 31	$	3,532		$	2,578		$	2,177