INCOME TAXES - Significant Components of Income Taxe Expense ( (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current tax expense:
Federal	$ 7,596	$ 5,415	$ 305
State	135	0	0
Total current tax expense	7,731	5,415	305
Deferred tax expense:
Federal	21,128	16,653	7,924
State	3,507	4,053	1,981
Total deferred tax expense	24,635	20,706	9,905
Income tax expense before change in deferred tax asset valuation allowance	32,366	26,121	10,210
Change in deferred tax asset valuation allowance	(296)	(126)	(4,797)
Income tax expense	$ 32,070	$ 25,995	$ 5,413