CAPITAL STOCK (Tables)

6 Months Ended

Jun. 30, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of weighted average valuation assumptions

The fair value of each option grant was estimated on the date of grant using the Black-Scholes option-pricing model with the following weighted average assumptions for options granted in the three and six months ended June 30,2018 and 2017.

	Three Months Ended June 30,		Six Months Ended June 30,
	2018	2017	2018	2017
Risk-free interest rate	2.76%	1.75%	2.64%	1.75%
Expected lives	4.9 years	4.9 years	4.9 years	4.9 years
Expected volatility	40%	41%	40%	41%
Expected dividend yield	0%	0%	0%	0%

Schedule of stock options plans

A summary of our stock option plans is as follows:

	Six Months Ended June 30,				Year Ended December 31,
	2018				2017
	Options		Weighted Average Exercise Price		Options		Weighted Average Exercise Price
Outstanding at beginning of period	630,847		$	29.312	829,617		$	23.203
Granted at market	131,000		$	69.887	27,050		$	99.087
Canceled	(19,374	)	$	52.158	(18,331	)	$	57.197
Exercised	(45,657	)	$	27.533	(207,489	)	$	11.520
Outstanding at end of period	696,816		$	36.421	630,847		$	29.312
Exercisable at end of period	449,097		$	19.854	456,802		$	18.316

Schedule of shares authorized under stock options plans by exercise price

The following table summarizes information about stock options outstanding and exercisable at June 30, 2018:

	Options Outstanding				Options Exercisable
Exercise Prices	Number of Options Outstanding at June 30, 2018	Weighted Average Remaining Contractual Life in Years	Weighted Average Exercise Price		Number of Options Exercisable at June 30, 2018	Weighted Average Exercise Price
$  4.40 - $  6.90	92,535	2.14	$	5.378	92,535	$	5.378
$  6.91 - $  8.55	158,623	5.08	$	7.771	158,623	$	7.771
$  8.56 - $ 39.56	130,030	6.57	$	22.467	117,582	$	22.650
$ 39.57 - $ 69.77	207,950	8.86	$	58.575	45,578	$	39.858
$ 69.78 - $ 108.25	107,678	8.62	$	79.372	34,779	$	77.817
$  4.40 - $ 108.25	696,816	6.64	$	36.421	449,097	$	19.854

Schedule of pricing models

The weighted average assumptions used for the periods presented were as follows:

	Three Months Ended June 30,		Six Months Ended June 30,
	2018	2017	2018	2017
Risk-free interest rate	1.09%	0.70%	1.06%	0.67%
Expected lives	1.2 years	1.2 years	1.2 years	1.2 years
Expected volatility	44%	45%	44%	45%
Expected dividend yield	0%	0%	0%	0%