STOCKHOLDERS' EQUITY Changes in Stockholders' Equity (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Beginning balance, shares			52,248,514
Stock option exercises, shares			143,514		851,720
Ending balance, shares	52,471,354		52,471,354		52,248,514
Beginning balance			$ 1,414,855
NET INCOME	58,984	51,183	156,569	139,620
Other comprehensive income (loss), net of tax	197	(1,316)	24,555	(5,440)
Ending balance	1,548,533		1,548,533		1,414,855
Parenthetical Disclosures
Dividends declared per common share	$ 0.4250	$ 0.3775	$ 1.1800	$ 1.0825
Total Stockholders' Equity
Beginning balance			1,414,855	1,258,892	1,258,892
NET INCOME			156,569	139,620
Repurchase and retirement of common stock			(4,508)	(4,896)
Dividends declared on common stock			(61,821)	(55,677)
Stock option exercises			6,860	3,796
Shares issued under the Employee Stock Purchase Plan			1,353	1,133
Share-based compensation, net of forfeitures			10,670	11,378
Other				403
Other comprehensive income (loss), net of tax			24,555	(5,440)
Ending balance	1,548,533	1,349,209	1,548,533	1,349,209
Common Stock
Beginning balance, shares			52,248,514	51,323,368	51,323,368
Repurchase and retirement of common stock, shares			(50,388)	(69,183)
Stock option exercises, shares			143,514	108,693
Shares issued under the Employee Stock Purchase Plan, shares			19,024	18,107
Issuance of restricted stock			121,811	153,381
Forfeiture of restricted stock			(11,121)	(9,929)
Ending balance, shares	52,471,354	51,524,437	52,471,354	51,524,437
Beginning balance			989,334	943,444	943,444
Repurchase and retirement of common stock			(4,508)	(4,896)
Stock option exercises			6,860	3,796
Shares issued under the Employee Stock Purchase Plan			1,353	1,133
Share-based compensation, net of forfeitures			10,670	11,378
Other				403
Ending balance	1,003,709	955,258	1,003,709	955,258
Retained Earnings
Beginning balance			443,569	330,816	330,816
NET INCOME			156,569	139,620
Dividends declared on common stock			(61,821)	(55,677)
Ending balance	538,317	414,759	538,317	414,759
Accumulated Other Comprehensive Income (Loss)
Beginning balance			(18,048)	(15,368)	(15,368)
Other comprehensive income (loss), net of tax			24,555	(5,440)
Ending balance	$ 6,507	$ (20,808)	$ 6,507	$ (20,808)