UNAUDITED INTERIM FINANCIAL INFORMATION (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Information Disclosure [Abstract]
Total revenues (1)	$ 149,844	[1]	$ 150,659	[1]	$ 147,733	[1]	$ 146,231	[1]	$ 151,683	[1]	$ 143,552	[1]	$ 138,466	[1]	$ 134,284	[1]	$ 594,467	$ 567,985	$ 511,842
Income before income tax expense	23,865		1,883		270		14,889		22,831		9,564		7,949		20,509		40,907	60,853	51,633
Income tax expense (benefit)	7,711		(346)		(744)		4,294		6,996		2,365		1,737		6,236		10,915	17,334	13,667
Net income	$ 16,154		$ 2,229		$ 1,014		$ 10,595		$ 15,835		$ 7,199		$ 6,212		$ 14,273		$ 29,992	$ 43,519	$ 37,966
Net income per common share - basic and diluted (2)	$ 1.19	[2]	$ 0.16	[2]	$ 0.08	[2]	$ 0.79	[2]	$ 1.20	[2]	$ 0.55	[2]	$ 0.48	[2]	$ 1.10	[2]	$ 2.23	$ 3.33	$ 2.95

[1] Amounts include the reclassification of foreign currency exchange rate gains (losses) to other income in the consolidated financial statements. Prior to the fourth quarter of 2014, these amounts were reported as a component of other expenses.

[2] 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.