Consolidated Statements of Changes in Shareholders' Equity (Parenthetical) (USD $)	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Statement Of Stockholders Equity [Abstract]
Stock option exercises (shares)	662,224	140,311
Issuance of preferred stock (shares)	6,000,000
Purchase of treasury stock, shares	1,905,077
Cash dividends declared on preferred stock, per share	$ 0.45
Cash dividends, per share	$ 0.98	$ 0.94