SHARE-BASED COMPENSATION Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number		1,015,627	543,377	906,991	1,116,308
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price		$ 23.55	$ 25.40	$ 19.78	$ 17.58
Share purchase options granted		522,250	57,386	40,683
Expiration period after the grant date		10 years	10 years	10 years
Grant date fair value of the options		$ 9.63	$ 8.71	$ 12.29
Total compensation cost related to non-vested options not yet recognized		$ 3.7	$ 0.0
Number of stock options exercised		50,000	421,000	250,000
Intrinsic value of options exercised		$ 0.1	$ 3.1	$ 4.8
Aggregate intrinsic value of options outstanding		$ 0.0	$ 0.5	$ 2.6	$ 16.8
Weighted average remaining contractual term for options outstanding		6 years 11 months	4 years 8 months	2 years 11 months	3 years
Number of stock options exercisable		535,627	472,042	851,020
Weighted-average exercise price		$ 25.66	$ 25.73	$ 19.22
Weighted-average remaining contractual term		4 years 7 months	4 years 1 month	2 years 7 months
Aggregate intrinsic value of options exercisable		$ 0.0	$ 0.4	$ 2.6
Number of options vested		113,585	42,022.000	38,998.000
Weighted average grant date fair value of options vested		$ 10.29	$ 11.90	$ 12.82
General and Administrative Expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense		$ 4.9	$ 4.0	$ 4.3
Anti-dilutive stock options outstanding
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense		$ 1.3	$ 0.9	0.5
Weighted average period for recognition		3 years 3 months	1 day
Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cliff vesting period after date of issuance		3 years
Stock Granted, Value, Share-based Compensation, Forfeited		$ 0.0	$ 0.5	0.1
Share-based compensation expense		3.3	3.1	3.6
Unrecognized compensation costs related to non-vested restricted shares		$ 3.5	$ 2.9	$ 3.7
Weighted average period for recognition		1 year 7 months	1 year 7 months	1 year 7 months
Total fair value of restricted shares vested		$ 4.5	$ 3.1	$ 3.2
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cliff vesting period after date of issuance		3 years
Share-based compensation expense		$ 0.2	$ (0.1)	$ 0.2
Vesting on Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage	100.00%	0.00%	25.00%
Vesting In Year 1
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		16.70%	25.00%
Vesting In Year 2
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		16.70%	25.00%
Vesting In Year 3
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		16.70%	25.00%
Director
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cliff vesting period after date of issuance		1 year
Chief Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date fair value of the options		$ 9.60
Chief Executive Officer [Member] | Vesting In Year 4
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		16.70%
Chief Executive Officer [Member] | Vesting In Year 5
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		16.70%
Chief Executive Officer [Member] | Vesting in Year 6
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		16.70%
Interim Chief Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date fair value of the options		$ 9.90
Common Class A [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share purchase options granted			57,386	40,683
Issuance of shares as a result of stock options exercised		5,011	156,022	158,925
Common Class A [Member] | Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares issued pursuant to stock incentive plan		125,371	153,648	78,685
Restricted shares forfeited by employees who left the Company prior to the vesting period		46,943	11,897	9,621
Common Class A [Member] | Director | Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares issued pursuant to stock incentive plan		41,396	39,288	28,215
Common Class A [Member] | Former Chief Executive Officer [Member] | Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares forfeited by employees who left the Company prior to the vesting period		46,319
Stock Granted, Value, Share-based Compensation, Forfeited	$ 0.0		$ 0.4
Common Class A [Member] | Chief Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share purchase options granted		480,000
Common Class A [Member] | Interim Chief Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share purchase options granted		42,250
Service Provider
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number			0
Service Provider | Common Class A [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of share purchase options granted to service provider (shares)		300,000	300,000