Stockholders' Equity and Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2016

Non-cash Stock-Based Compensation Resulting from Employee Restricted Common Stock Agreements

The following table presents non-cash stock-based compensation expense resulting from employee restricted common stock agreements and is presented in the following line items in the accompanying consolidated statements of income for the years ended December 31, 2016, 2015 and 2014 (dollars in thousands):

Years Ended December 31,	2016		2015		2014
Operating expense	$	2,217	$	235	$	32
Sales and marketing		3,656	559		166
Research and development		836	104		16
General and administrative		15,837	2,112		498
Total non-cash stock-based compensation expense	$	22,546	$	3,010	$	712

Nonvested Restricted Stock Unit Awards

The following table presents a summary of the activity related to restricted stock for the years ended December 31, 2016 and 2015: 

Year ended December 31, 2015	Number of shares			Weighted average grant- date fair value (in dollars)
Unvested shares of restricted stock outstanding at January 1, 2015		4,540,020		$	0.24
2015 Restricted Stock granted		741,931			27.65
2014 Restricted Stock vested		(3,287,091	)		0.20
2015 Restricted Stock forfeited		(7,805	)		30.95
2014 Restricted Stock forfeited		(7,215	)		0.48
Unvested shares of restricted stock outstanding at December 31, 2015		1,979,840			10.45
2016 Restricted Stock granted		1,575,429			32.14
2016 Restricted Stock vested		(490,700	)		23.15
2015 Restricted Stock vested		(271,397	)		28.07
2014 Restricted Stock vested		(571,313	)		0.31
2016 Restricted Stock forfeited		(25,317	)		36.11
2015 Restricted Stock forfeited		(22,449	)		29.43
2014 Restricted Stock forfeited		(6,154	)		0.54
Unvested shares of restricted stock outstanding at December 31, 2016		2,167,939		$	23.33

Post-IPO Restricted Stock [Member]

Summary of Grant-Date Fair Values of Post-IPO Restricted Stock Granted and Related Assumptions

The following table presents a summary of the grant-date fair values of Post-IPO Restricted Stock granted during the years ended December 31, 2016 and 2015 and the related assumptions:

Years Ended December 31,	2016		2015
Grant-date fair value of restricted stock	$23.15 - $49.34		$21.76 - $33.33
Risk-free interest rates (based on U.S. Treasury Securities from 5 to 10 years maturity)	1.28% - 1.36%			2.2%
Estimated volatility	21.0% - 23.0%			26.0%
Expected life (in years)		2.7		3.6
Dividend yield	0%		0%