SHARE-BASED PAYMENT - Plan Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restricted shares
Restricted Shares - Shares
Nonvested at beginning of period (in shares)	1,344,523
Granted (in shares)	434,357
Vested (in shares)	(571,531)
Forfeited (in shares)	(36,331)
Nonvested at end of period (in shares)	1,171,018	1,344,523
Restricted Shares - Weighted Average Grant-date Fair Value
Nonvested at beginning of period (in dollars per share)	$ 26.68
Granted (in dollars per share)	52.25	$ 41.15	$ 21.51
Vested (in dollars per share)	23.75
Forfeited (in dollars per share)	35.32
Nonvested at end of period (in dollars per share)	$ 37.32	$ 26.68
Additional disclosures
Fair value, vested shares (in dollars)	$ 29,600	$ 21,200	$ 10,300
Unrecognized compensation
Unrecognized compensation for outstanding restricted shares/units	$ 23,400
Unrecognized compensation cost, period for recognition	2 years 7 months 6 days
Stock options
Options
Outstanding at beginning of period (in shares)	1,396,706
Granted (in shares)	0
Exercised (in shares)	(348,442)
Outstanding at end of period (in shares)	1,048,264	1,396,706
Exercisable at end of period (in shares)	904,055
Weighted Average Exercise Price
Outstanding at beginning of period (in dollars per share)	$ 18.85
Exercised (in dollars per share)	16.12
Outstanding at end of period (in dollars per share)	19.76	$ 18.85
Exercisable at end of period (in dollars per share)	$ 18.04
Weighted-Average Remaining Contract Life (Years)
Outstanding at end of period (in years)	5 years 7 months 6 days
Exercisable at end of period (in years)	4 years 10 months 24 days
Aggregate Intrinsic Value
Outstanding at end of period (in dollars)	$ 23,685
Exercisable at end of period (in dollars)	21,979
Intrinsic value of options exercised, (in dollars)	13,500	$ 400	200
Cash received from the exercise of options	0	$ 0	$ 0
Unrecognized compensation
Unrecognized compensation cost for outstanding options	$ 700
Unrecognized compensation cost, period for recognition	1 year
RSUs
Restricted Shares - Shares
Nonvested at beginning of period (in shares)	861,318
Granted (in shares)	280,237
Vested (in shares)			0	0
Forfeited (in shares)	(42,943)
Nonvested at end of period (in shares)	1,098,612	861,318
Restricted Shares - Weighted Average Grant-date Fair Value
Nonvested at beginning of period (in dollars per share)	$ 30.89
Granted (in dollars per share)	49.72	$ 41.79	$ 23.92
Forfeited (in dollars per share)	34.94
Nonvested at end of period (in dollars per share)	$ 35.54	$ 30.89
Additional disclosures
Fair value, vested shares (in dollars)		$ 23,100
Unrecognized compensation
Unrecognized compensation for outstanding restricted shares/units	$ 6,200
Unrecognized compensation cost, period for recognition	1 year 2 months 12 days