QUARTERLY FINANCIAL INFORMATION (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
QUARTERLY FINANCIAL INFORMATION (UNAUDITED)
Total revenues	$ 300,983	$ 258,736	$ 308,639	$ 231,762	$ 278,546	$ 242,265	$ 273,514	$ 240,680	$ 1,100,120	$ 1,035,005	$ 797,088
Operating income	62,443	24,372	54,133	77,554	59,372	784	73,636	192,970	218,502	326,762	118,764
Net income	147,328	10,516	3,120	5,659	43,595	7,996	6,970	143,765	166,623	202,326	126,719
Net income attributable to common stockholders	$ 149,121	$ 10,504	$ 3,120	$ 5,659	$ 43,595	$ 7,973	$ 6,970	$ 143,765	$ 168,404	$ 202,303	$ 126,719
EARNINGS PER SHARE
Basic earnings (loss) per share: (in dollars per share)	$ 3.48	$ 0.25	$ 0.08	$ 0.14	$ 1.10	$ 0.20	$ 0.18	$ 3.64	$ 4.07	$ 5.12	$ 3.21
Diluted earnings (loss) per share: (in dollars per share)	$ 3.46	$ 0.24	$ 0.07	$ 0.13	$ 1.02	$ 0.19	$ 0.16	$ 2.69	$ 3.91	$ 4.73	$ 1.60
Weighted average shares outstanding:
Basic (in shares)	42,860,000	42,845,000	40,373,000	39,799,000	39,502,000	39,502,000	39,492,000	39,473,000	41,364	39,492	39,470
Diluted (in shares)	43,120,000	43,267,000	43,051,000	42,757,000	42,753,000	42,760,000	42,664,000	42,400,000	43,089	42,729	42,754