Equity (Details) (USD $) In Thousands, except Share data, unless otherwise specified	1 Months Ended			12 Months Ended
	Feb. 28, 2011	Mar. 31, 2010	Jun. 30, 2009	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Equity (Textual)
Number of common shares issued to qualified pension plan		1,190,000
Common stock, par value		$ 1	$ 1	$ 1	$ 1	$ 1
Increase in equity from issuance of common shares to pension plan		$ 53,864,000
Value of common shares issued to pension plan		1,190,000
Increase in capital in excess of par from issuance of common shares to pension plan		52,674,000
Common stock issued in connection with business acquisitions	372,992			372,992		789,495
Net of acquired cash, shares	368,527			368,527
Number of common shares issued in a public offering			13,225,000
Price of common shares			$ 41.00
Shares issued upon full exercise of the underwriters' option to purchase additional shares			1,725,000
Net proceeds from the sale of the shares in a public offering			519,993,000
Commissions and transaction costs included in net proceeds			22,232,000
Increase in equity from issuance of common shares in a public offering			519,993,000
Value of common shares issued in a public offering			13,225,000
Increase in capital in excess of par from issuance of common shares in a public offering			506,768,000
Shares of common stock issued to trustee under 401(k) savings and retirement plan				110,881	882,131	1,135,510
Net proceeds from issuance of common stock to the trustee under 401(k) savings and retirement plan				$ 4,745	$ 41,734	$ 52,691
Number of shares held in treasury
Number of treasury shares purchased
Shares remaining under the current authorization repurchase program				3,411,416