QUARTERLY SUPPLEMENTARY FINANCIAL INFORMATION (UNAUDITED) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended															12 Months Ended
	Dec. 31, 2013		Sep. 30, 2013	Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2013	Dec. 31, 2012		Dec. 31, 2011
Quarterly Financial Data [Abstract]
Revenues	$ 228,994		$ 223,024	$ 219,719		$ 205,305		$ 213,317		$ 206,581		$ 199,646		$ 193,699		$ 877,042	$ 813,243		$ 705,008
Income (loss) before income taxes	37,339		14,395	20,318		29,850		(7,999)		10,020		19,177		24,876		101,902	46,074		(12,715)
Net income (loss)	$ 26,526		$ 11,725	$ 15,496		$ 22,393		$ (2,418)		$ 8,730		$ 14,716		$ 19,184		$ 76,140	$ 40,212		$ 11
Basic earnings (loss) per share (in usd per share)	$ 1.04	[1]	$ 0.46	$ 0.61	[1]	$ 0.89	[1]	$ (0.10)	[1]	$ 0.34	[1]	$ 0.58	[1]	$ 0.75	[1]	$ 3.01	$ 1.58	[1]	$ 0.00
Diluted earnings (loss) per share (in usd per share)	$ 1.04	[1]	$ 0.45	$ 0.61	[1]	$ 0.88	[1]	$ (0.10)	[1]	$ 0.34	[1]	$ 0.58	[1]	$ 0.75	[1]	$ 2.98	$ 1.58	[1]	$ 0.00

[1] The sum of the quarterly reported amounts may not equal the full year, as each is computed independently.