CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (Parenthetical) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Stockholders' Equity Attributable to Parent
Common dividends declared - per share (in dollars per share)	$ 2.1	$ 2.08	$ 2.08
Issuance of shares of common stock, common stock offering, net of expenses (in shares)	2,179,153	586,977	0
Issuance of shares of common stock, options exercised (in shares)	4,500	9,250	18,000
Issuance of shares of common stock, dividend reinvestment plan (in shares)	3,915	5,989	6,705
Withheld shares of common stock to satisfy tax withholding obligations in connection with the vesting of restricted stock (in shares)	36,195	3,564	19,668