Condensed Consolidated Statements of Stockholders' Equity (Parenthetical) - $ / shares	6 Months Ended
	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014
Statement of Stockholders' Equity [Abstract]
Cash dividends declared per common share (in dollars per share)	$ 0.3	$ 0.280	$ 0.265
Common stock issued per share for stock bonus (in dollars per share)	$ 34.32	$ 0	$ 35.87