CAPITAL STOCK (Tables)

6 Months Ended

Jun. 30, 2019

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 30,2019 and 2018.

	Three Months Ended June 30,		Six Months Ended June 30,
	2019	2018	2019	2018
Risk-free interest rate	1.89%	2.76%	1.95%	2.64%
Expected lives	4.7 years	4.9 years	4.7 years	4.9 years
Expected volatility	40%	40%	40%	40%
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,
	2019				2018
	Options		Weighted Average Exercise Price		Options		Weighted Average Exercise Price
Outstanding at beginning of period	620,553		$	40.741	630,847		$	29.312
Granted at market	11,200		$	73.193	153,700		$	75.244
Forfeited	(256	)	$	98.660	(18,978	)	$	53.010
Expired	—		$	—	(896	)	$	65.414
Exercised	(149,828	)	$	16.776	(144,120	)	$	25.740
Outstanding at end of period	481,669		$	48.920	620,553		$	40.741
Exercisable at end of period	305,452		$	33.655	386,176		$	21.214

The following table summarizes restricted stock transactions for the six months ended June 30, 2019:

	RSAs		Weighted-Average Grant Date Fair Value Per Award
Non-vested as of December 31, 2018	259,430		$	74.26
Granted	18,567		71.38
Vested	(4,230	)	85.09
Forfeited	(500	)	80.90
Non-vested as of June 30, 2019	273,267		$	73.90

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, 2019:

	Options Outstanding				Options Exercisable
Exercise Prices	Number of Options Outstanding at June 30, 2019	Weighted Average Remaining Contractual Life in Years	Weighted Average Exercise Price		Number of Options Exercisable at June 30, 2019	Weighted Average Exercise Price
$ 4.96 - $ 7.36	93,352	3.65	$	6.998	93,352	$	6.998
$ 7.37 - $ 32.21	79,273	4.79	$	15.897	78,941	$	15.828
$ 32.22 - $ 62.50	57,533	6.57	$	39.797	46,524	$	39.724
$ 62.51 - $ 69.77	130,000	8.68	$	69.770	43,337	$	69.770
$ 69.78 - $ 108.25	121,511	8.10	$	84.684	43,298	$	80.960
$ 4.96 - $ 108.25	481,669	6.67	$	48.920	305,452	$	33.655

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,
	2019	2018	2019	2018
Risk-free interest rate	2.21%	1.09%	2.27%	1.06%
Expected lives	1.1 years	1.2 years	1.1 years	1.2 years
Expected volatility	39%	44%	39%	44%
Expected dividend yield	0%	0%	0%	0%