Accounting for Stock-Based Compensation (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Summary of changes in outstanding stock options
Shares, Outstanding, Beginning Balance	460,653	392,369	312,973
Shares, Exercised	(11,521)	(39,487)	(110,237)
Shares, Granted	203,436	190,552	196,133
Shares, Forfeited/Expired	(13,768)	(82,781)	(6,500)
Shares, Outstanding, Ending Balance	638,800	460,653	392,369
Weighted Average Exercise Price, Beginning Balance	$ 20.50	$ 19.32	$ 12.12
Weighted Average Exercise Price, Exercised	$ 6.73	$ 12.11	$ 8.76
Weighted Average Exercise Price, Granted	$ 25.39	$ 21.77	$ 24.44
Weighted Average Exercise Price, Forfeited/Expired	$ 24.58	$ 21.85	$ 6.16
Weighted Average Exercise Price, Ending Balance	$ 22.21	$ 20.50	$ 19.32
Aggregate Intrinsic Value, Beginning Balance	$ 1,972	$ 2,511	$ 4,594
Aggregate Intrinsic Value, Exercised	(193)	(500)	(1,870)
Aggregate Intrinsic Value, Granted	0	574	251
Aggregate Intrinsic Value, Forfeited/Expired	0	(243)	(127)
Aggregate Intrinsic Value, Ending Balance	786	1,972	2,511
Shares, Vested plus expected to vest	625,762
Weighted Average Exercise Price, Vested plus expected to vest	$ 22.16
Aggregate Intrinsic Value, Vested plus expected to vest	801
Shares, Exercisable	293,896
Weighted Average Exercise Price, Exercisable	$ 22.21	$ 20.50	$ 19.32
Aggregate Intrinsic Value, Exercisable	$ 1,035