SHAREHOLDERS' EQUITY (Details) (USD $)	12 Months Ended			1 Months Ended		12 Months Ended			1 Months Ended				12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Oct. 31, 2010 RSU	Mar. 31, 2009 RSU	Dec. 31, 2011 RSU	Dec. 31, 2010 RSU	Dec. 31, 2009 RSU	May 31, 2011 RSA	May 31, 2010 RSA	May 31, 2009 RSA	May 31, 2008 RSA	Dec. 31, 2011 RSA	Dec. 31, 2011 SAR years	Dec. 31, 2010 SAR	Dec. 31, 2009 SAR
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Public offering of common stock, shares			3,750,000
Public offering of common stock, price per share			$ 27
Public offering of common stock, net proceeds			$ 95,731,000
Public offering of common stock, underwriting commission and offering expenses			5,500,000
Number of issuable common shares	2,654,000
Summary of Activity of RSU, RSA and SAR [Rollforward]
Outstanding						594,000							4,200	1,822,079
Granted				454,000	300,000	0							5,046
Forfeited														(10,000)
Vested						0							(4,200)
Outstanding						594,000	594,000						5,046	1,812,079	1,822,079
Unrecognized compensation cost (in dollars)						10,023							62		0
Total fair value of RSU grants				13,900,000	5,900,000
Stock-based compensation expense						$ 4,404,982	$ 3,800,000	$ 1,600,000						$ 0	$ 728,000	$ 2,800,000
RSA issued to each non-employee director									700	700	700	700
Fair Value Assumptions and Methodology
Expected volatility, minimum														29.00%
Expected volatility, maximum														31.00%
Expected term (in years)														7
Risk-free rate, minimum														4.30%
Risk-free rate, maximum														4.70%
Expected dividend yield														0.00%
Expected forfeiture rate														0.00%
Expired														(10,000)
Weighted Average Exercise Price, Outstanding														$ 36.16	$ 36.15
Weighted Average Exercise Price, Expired														$ 33.76
Weighted Average Contractual Term Remaining, Outstanding (in years)														4.5	5.5