SHAREHOLDERS' EQUITY (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Feb. 21, 2018	May 31, 2017	Feb. 25, 2016	Jan. 14, 2016	May 07, 2014	Jan. 11, 2010
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Annual interest rate on convertible senior notes				0.625%
Calculation of weighted average common shares
Weighted average common shares, basic	12,090,000	11,827,000
Effect of dilutive securities
Effect of stock options (in shares)	1,559,000	1,553,000
Effect of dilutive share awards (in shares)	213,000	97,000
Effect of Convertible Senior Notes (in shares)	986,000	0
Weighted average common shares, diluted	14,848,000	13,477,000
Common stock repurchases
Value of common stock authorized to be repurchased			$ 100,000,000		$ 40,000,000	$ 50,000,000	$ 10,000,000	$ 10,000,000
Purchase of treasury stock (in shares)	30,416
Remaining authorized repurchase amount	$ 116,700,000
Employee stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	300,000	0