EARNINGS PER COMMON SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Basic and Diluted Earnings per Share [Line Items]
Net income	$ 30,895	$ 19,534	$ 15,018	$ 23,679	$ 34,796	$ 325	$ 10,685	$ 13,331	$ 89,126	$ 59,137	$ 76,140
Weighted-average common shares outstanding (in shares)									25,047,405	25,230,854	25,325,695
Weighted-average common shares, Diluted (in shares)									25,235,996	25,493,663	25,531,375
Basic earnings per common share (in usd per share)	$ 1.23	$ 0.78	$ 0.60	$ 0.95	$ 1.39	$ 0.01	$ 0.42	$ 0.53	$ 3.56	$ 2.34	$ 3.01
Diluted earnings per common share (in usd per share)	$ 1.21	$ 0.77	$ 0.59	$ 0.94	$ 1.38	$ 0.01	$ 0.42	$ 0.52	$ 3.53	$ 2.32	$ 2.98
Awards excluded from diluted calculation (in shares)									343,390	835,610	638,478
Restricted Stock Awards [Member]
Basic and Diluted Earnings per Share [Line Items]
Add dilutive effect of restricted stock awards (in shares)									122,840	114,313	59,849
Stock Options [Member]
Basic and Diluted Earnings per Share [Line Items]
Add dilutive effect of restricted stock awards (in shares)									65,751	148,496	145,831