EARNINGS PER SHARE (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2012	Mar. 31, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Basic Earnings Per Share:
Net earnings	$ 15,557	$ 5,264	$ 12,841	$ 20,821	$ 23,517
Less: earnings allocated to unvested restricted stock	(538)	(122)	(600)	(602)	(976)
Net earnings allocated to common shares	15,019	5,142	12,241	20,219	22,541
Weighted-average basic shares and unvested restricted stock outstanding	37,359,200	37,284,000	37,239,800	37,321,600	37,021,900
Less: weighted-average unvested restricted stock outstanding (in shares)	(1,669,200)	(1,654,000)	(1,768,200)	(1,661,600)	(1,559,000)
Weighted-average basic shares outstanding	35,690,000	35,630,000	35,471,600	35,660,000	35,462,900
Basic earnings per share (in dollars per share)	$ 0.42	$ 0.14	$ 0.35	$ 0.57	$ 0.64
Diluted Earnings Per Share:
Net earnings allocated to common shares	$ 15,019	$ 5,142	$ 12,241	$ 20,219	$ 22,541
Weighted-average basic shares outstanding	35,690,000	35,630,000	35,471,600	35,660,000	35,462,900
Diluted earnings per share (in dollars per share)	$ 0.42	$ 0.14	$ 0.35	$ 0.57	$ 0.64