Employee Stock Benefit Plans (Nonvested Stock Option Activity) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares [Roll Forward]
Nonvested at beginning of period	422,757	550,120	573,369
Granted	163,042	168,939	220,007
Vested	(202,115)	(283,185)	(221,065)
Forfeited	(36,093)	(13,117)	(22,191)
Nonvested at end of period	347,591	422,757	550,120
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Nonvested at beginning of period, weighted-average value (in USD per share)	$ 7.53	$ 4.81	$ 3.74
Granted, weighted-average value (in USD per share)	$ 9.33	$ 12.58	$ 8.33
Vested, weighted-average value (in USD per share)	$ 5.76	$ 6.87	$ 5.57
Forfeited, weighted-average value (in USD per share)	$ 10.40	$ 7.02	$ 4.26
Nonvested at end of period, weighted-average value (in USD per share)	$ 9.11	$ 7.53	$ 4.81