UNAUDITED INTERIM FINANCIAL INFORMATION (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
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 147,479		$ 165,104		$ 158,808		$ 152,335		$ 149,844		$ 150,659		$ 147,733		$ 146,231		$ 623,726	$ 594,467	$ 567,985
Income before income tax expense	13,923		15,921		11,875		29,937		23,865		1,883		270		14,889		71,656	40,907	60,853
Income tax expense (benefit)	4,028		4,732		3,127		9,607		7,711		(346)		(744)		4,294		21,494	10,915	17,334
Net income	$ 9,895		$ 11,189		$ 8,748		$ 20,330		$ 16,154		$ 2,229		$ 1,014		$ 10,595		$ 50,162	$ 29,992	$ 43,519
Net income per common share - basic and diluted (1)	$ 0.48	[1]	$ 0.54	[1]	$ 0.42	[1]	$ 1.00	[1]	$ 0.80	[1]	$ 0.11	[1]	$ 0.05	[1]	$ 0.53	[1]	$ 2.43	$ 1.48	$ 2.22

[1] Since the weighted-average number of shares outstanding for the quarters are calculated independently of the weighted-average number of shares outstanding for the year, quarterly net income per share may not total to annual net income per share.