CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Parenthetical) (USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY      
Issuance of shares of treasury stock for employee stock purchase plan 37,836 22,493 23,640
Issuance of shares of treasury stock for restricted stock unit vesting and related tax benefit 18,618 111,012 6,804
Cash dividends, common stock (in dollars per share) $ 0.19 $ 0.12 $ 0.24
Stock dividends, restricted stock units (in dollars per share) $ 0.19 $ 0.12 $ 0.24