CAPITAL STOCK - OPTION ACTIVITY (Details) - $ / shares	3 Months Ended	12 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate (as a percent)	0.72%	2.45%
Expected lives (in years)	4 years 6 months	4 years 8 months 12 days
Expected volatility (as a percent)	39.00%	39.00%
Expected dividend rate (as a percent)	0.00%	0.00%
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding at beginning of period	536,315
Granted at market	250		88,200
Forfeited	(35,641)		(1,353)
Expired	(1,051)		(716)
Exercised	(10,483)		(170,369)
Outstanding at end of period	489,390		536,315
Exercisable at end of period	339,845		315,964
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Outstanding at beginning of period (in dollars per share)	$ 54.855
Granted at market (in dollars per share)	95.660		$ 84.234
Forfeited (in dollars per share)	70.546		98.660
Expired (in dollars per share)	98.660		98.660
Exercised (in dollars per share)	8.779		18.125
Outstanding at ending of period (in dollars per share)	54.626		54.855
Exercisable at end of period (in dollars per share)	$ 41.893		$ 37.644
Employee Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate (as a percent)	1.34%	2.35%
Expected lives (in years)	1 year 1 month 6 days	1 year 1 month 6 days
Expected volatility (as a percent)	44.00%	40.00%
Expected dividend rate (as a percent)	0.00%	0.00%

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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- Definition

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.