Share-Based Compensation - Summary of Stock Option Activity (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Summary of stock option activity
Options outstanding, Beginning Balance, Shares	314,323	363,896	584,201
Options outstanding, Beginning Balance, Weighted Average Exercise Price	$ 19.79	$ 22.03	$ 23.32
Options outstanding, Beginning Balance, Options Exercisable	314,323	276,009	396,688
Exercised, Shares	(66,076)	(59,543)	(12,099)
Exercised, Weighted Average Exercise Price	$ 18.53	$ 19.42	$ 19.41
Shares Forfeited or Expired	(18,522)	(15,853)	(208,206)
Weighted Average Exercise Price Forfeited	$ 35.28	$ 40.45	$ 25.81
Options outstanding, Ending Balance, Shares	247,590	314,323	363,896
Options outstanding, Ending Balance, Weighted Average Exercise Price	$ 17.82	$ 19.79	$ 22.03
Options outstanding, Ending Balance, Options Exercisable	247,590	314,323	276,009
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	0	0	0
Additional Shares Granted from Special Dividend	17,865	25,823