Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Fair Values of Options Granted Estimated Using Weighted-Average Assumptions

The Company uses the Black-Scholes option pricing model to calculate the grant-date fair value of an award. The Company calculated the fair values of the options granted using the following estimated weighted-average assumptions:

	Years Ended December 31,
	2018			2017			2016
Expected volatility		39	%		43	%		46	%
Expected term	6 years			6 years			6 years
Risk-free interest rate		2.82	%		1.87	%		1.90	%
Expected dividend yield		—	%		—	%		—	%
Weighted-average grant date fair value per share	$	11.94		$	4.61		$	3.91

Summary of Stock Option Activity Under Company's Stock Option Plans

A summary of the stock option activity under the Company’s stock option plans for the year ended December 31, 2018 is presented below:

	Options Outstanding			Weighted-Average Exercise Price Per Share		Weighted-Average Remaining Contractual Term in Years		Aggregate Intrinsic Value
Options outstanding at December 31, 2017		344,090		$	6.41
Granted		20,000			28.42
Exercised		(178,090	)		5.64			$	2,704
Forfeited		—			—
Canceled		—			—
Options outstanding at December 31, 2018		186,000		$	9.50		4.32	$	828
Options exercisable at December 31, 2018		166,000		$	7.22		3.70	$	828
Options vested or expected to vest at    December 31, 2018		184,108		$	9.31		4.26	$	828

Summary of Restricted Stock Unit Award Activity Under Company's Plans

Restricted stock unit awards are valued at the market price of a share of the Company’s common stock on the date of the grant. A summary of the restricted stock unit award activity under the Company’s plans for the year ended December 31, 2018 is presented below:

	Shares			Weighted-Average Grant Date Fair Value Per Share		Aggregate Intrinsic Value
Nonvested outstanding at December 31, 2017		1,414,000		$	9.37
Granted		542,202			27.59
Vested		(752,941	)		9.26
Forfeited		(6,000	)		9.57
Nonvested outstanding at December 31, 2018		1,197,261		$	17.69	$	14,619