Stock-Based Compensation - Share Option Activity (Details) (Stock Options [Member], USD $)	6 Months Ended		12 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding (in shares)	312,000
Grants in period (in shares)	0	0
Exercised (in shares)	(39,125)
Forfeited or expired (in shares)	(3,625)
Outstanding (in shares)	269,250		312,000
Exercisable (in shares)	55,125
Vested or expected to vest (in shares)	256,204
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Outstanding, weighted-average exercise price (in dollars per share)	$ 9.33
Granted, weighted-average exercise price (in dollers per share)	$ 0.00
Exercised, weighted-average exercise price (in dollars per share)	$ 7.80
Forfeited or expired, weighted-average exercise price (in dollars per share)	$ 7.80
Outstanding, weighted-average exercise price (in dollars per share)	$ 9.58		$ 9.33
Exercisable, weighted-average exercise price (in dollars per share)	$ 8.43
Vested or expected to vest, weighted-average exercise price (in dollars per share)	$ 9.54
Outstanding, average remaining contractual term (in years)	8 years 4 months 24 days		8 years 10 months 24 days
Outstanding, average remaining contractual term (in years)	8 years 4 months 24 days		8 years 10 months 24 days
Exercisable, average remaining contractual term (in years)	8 years 1 month 6 days
Vested or expected to vest, average remaining contractual term (in years)	8 years 4 months 24 days
Outstanding, aggregate intrinsic value	$ 1,946,000
Outstanding, aggregate intrinsic value	2,661,000		1,946,000
Exercisable, aggregate intrinsic value	608,000
Vested or expected to vest, aggregate intrinsic value	2,541,000
Total intrinsic value of share options exercised	$ 500,000