Stock-Based Compensation (Details 1) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Granted, Number of options	54,500	157,500	500,000
Exercisable at December 31, 2012, Weighted average exercise price	$ 17.57	$ 13.18	$ 7.52
Non Qualified Stock Option [Member]
Outstanding at December 31, 2011, Number of options	1,441,370
Granted, Number of options	54,500
Exercised, Number of options	(812,340)
Forfeited, Number of options	(37,100)
Expired, Number of options	(21,730)
Outstanding at December 31, 2012, Number of options	624,700
Stock options expected to vest, Number of options	610,500
Exercisable at December 31, 2012, Number of options	188,200
Outstanding at December 31, 2011, Weighted average exercise price	$ 9.93
Granted, Weighted average exercise price	$ 17.57
Exercised, Weighted average exercise price	$ 10.80
Forfeited, Weighted average exercise price	$ 11.74
Expired, Weighted average exercise price	$ 4.65
Outstanding at December 31, 2012, Weighted average exercise price	$ 9.54
Stock options expected to vest, Weighted average exercise price	$ 9.55
Exercisable at December 31, 2012, Weighted average exercise price	$ 8.49
Outstanding at December 31, 2012, Weighted average remaining contractual term	3 years 4 months 13 days
Stock options expected to vest, Weighted average remaining contractual term	3 years 4 months 13 days
Exercisable at December 31, 2012, Weighted average remaining contractual term	2 years 10 months 24 days
Outstanding at December 31, 2012, Aggregate intrinsic value	$ 6,942,000
Stock options expected to vest, Aggregate intrinsic value	6,774,000
Exercisable at December 31, 2012, Aggregate intrinsic value	$ 2,288,000