Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

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 stock options granted during each of the last three years:

	For the Years Ended December 31,
	2017	2016		2015
Risk-free interest rate	n/a	1.4	%	1.8	%
Expected term (in years)	n/a	5.8		6.0
Estimated dividend yield	n/a	—	%	—	%
Estimated volatility	n/a	48.8	%	41.8	%

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, 2017, 2016 and 2015, is as follows (in thousands):

	2017			2016			2015
Beginning balance, January 1	$	3,532		$	2,578		$	2,177
Additions and adjustments	7,680			3,165			1,368
Write-offs	(3,734		)	(2,211		)	(967		)
Ending balance, December 31	$	7,478		$	3,532		$	2,578