Stockholders' Equity Treasury Stock (Details)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Equity, Class of Treasury Stock [Line Items]
Balance at beginning of year	13,122,956	13,220,832	13,441,328
Shares issued to fund stock option exercises	(46,100)	(54,209)	(141,728)
Employee stock purchase plan shares issued	(33,402)	(42,391)	(44,319)
Nonvested shares issued	(121,865)	(5,723)	(56,136)
Nonvested shares forfeited	38,266	4,447	21,687
Balance at end of year	12,959,855	13,122,956	13,220,832