Share Based Compensation (Details 1) (USD $)	6 Months Ended
	Jun. 30, 2012
Summary of options outstanding
Weighted Average Remaining Contractual Life (Years)	5 years 7 months 13 days
Outstanding, Number	232,000
Exercisable, Number	197,000
Weighted Average Exercise Price, Ending balance	$ 16.12
5.34-5.39 [Member]
Summary of options outstanding
Range of Exercise Prices, minimum	$ 5.34
Range of Exercise Prices, maximum	$ 5.39
Weighted Average Remaining Contractual Life (Years)	9 years 4 months 28 days
Outstanding, Number	37,500
Exercisable, Number	2,500
Weighted Average Exercise Price	$ 5.34
14.47-15.34 [Member]
Summary of options outstanding
Range of Exercise Prices, minimum	$ 14.47
Range of Exercise Prices, maximum	$ 15.34
Weighted Average Remaining Contractual Life (Years)	5 years 7 months 6 days
Outstanding, Number	82,000
Exercisable, Number	82,000
Weighted Average Exercise Price	$ 14.47
15.35-16.50 [Member]
Summary of options outstanding
Range of Exercise Prices, minimum	$ 15.35
Range of Exercise Prices, maximum	$ 16.50
Weighted Average Remaining Contractual Life (Years)	4 years 8 months 16 days
Outstanding, Number	52,500
Exercisable, Number	52,500
Weighted Average Exercise Price	$ 15.78
16.51-19.10 [Member]
Summary of options outstanding
Range of Exercise Prices, minimum	$ 16.51
Range of Exercise Prices, maximum	$ 19.10
Weighted Average Remaining Contractual Life (Years)	3 years 7 months 2 days
Outstanding, Number	30,000
Exercisable, Number	30,000
Weighted Average Exercise Price	$ 19.10
19.11-19.17 [Member]
Summary of options outstanding
Range of Exercise Prices, minimum	$ 19.11
Range of Exercise Prices, maximum	$ 19.17
Weighted Average Remaining Contractual Life (Years)	2 years 7 months 2 days
Outstanding, Number	30,000
Exercisable, Number	30,000
Weighted Average Exercise Price	$ 19.17