Summary of Significant Accounting Policies - Earnings Per Share (Details)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	675,665	1,271,149
Restricted Shares [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Incremental Common Shares Attributable to Share-based Payment Arrangements	219,911	130,314	118,841
Stock Options [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Incremental Common Shares Attributable to Share-based Payment Arrangements	208,175	403,090	554,974
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	675,665	1,271,149	1,742,086