Stock Option Activity (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Share-based Arrangements with Employees and Nonemployees [Abstract]
Stock Option Vesting Period			4 years	4 years
Shares outstanding at beginning of period	2,540,677	3,150,144	2,621,686	3,331,031
Shares granted	77,500	72,500	157,000	113,900
Shares exercised	(106,781)	(179,250)	(204,090)	(285,444)
Shares forfeited or expired	(141,311)	(68,781)	(204,511)	(184,874)
Shares outstanding at end of period	2,370,085	2,974,613	2,370,085	2,974,613
Weighted average exercise price of options outstanding at beginning of period	$ 13.24	$ 12.07	$ 13.03	$ 11.91
Weighted average exercise price of options granted	$ 16.52	$ 16.16	$ 15.90	$ 17.17
Weighted average exercise price of options exercised	$ 7.82	$ 4.88	$ 7.05	$ 5.36
Weighted average exercise price of options forfeited or expired	$ 16.00	$ 17.63	$ 16.81	$ 16.20
Weighted average exercise price of options outstanding at end of period	$ 13.42	$ 12.48	$ 13.42	$ 12.48