Consolidated Statements of Changes in Shareholders' Equity (Parenthetical) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Stock option exercises (shares)	395,425	108,800
Issuance of preferred stock (shares)	6,000,000
Purchase of treasury stock, shares	1,905,077
Cash dividends declared on common stock, per share	$ 0.48	$ 0.46