Stock-Based Compensation - Share Option Activity (Details) (Stock Options [Member], USD $)	6 Months Ended		12 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding (in shares)	247,650
Exercised (in shares)	(58,150)
Forfeited or expired (in shares)	(94,250)
Outstanding (in shares)	95,250		247,650
Exercisable (in shares)	53,750
Vested or expected to vest (in shares)	94,499
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)	$ 9.59
Exercised, weighted-average exercise price (in dollars per share)	$ 9.53
Forfeited or expired, weighted-average exercise price (in dollars per share)	$ 10.84
Outstanding, weighted-average exercise price (in dollars per share)	$ 8.40		$ 9.59
Exercisable, weighted-average exercise price (in dollars per share)	$ 8.29
Vested or expected to vest, weighted-average exercise price (in dollars per share)	$ 8.40
Outstanding, average remaining contractual term (in years)	6 years 8 months 12 days		8 years
Exercisable, average remaining contractual term (in years)	6 years 3 months 18 days
Vested or expected to vest, average remaining contractual term	6 years 8 months 12 days
Outstanding, aggregate intrinsic value	$ 2,221,000		$ 2,015,000
Exercisable, aggregate intrinsic value	1,260,000
Vested or expected to vest, aggregate intrinsic value	2,204,000
Total instrinsic value of share options exercised	900,000
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	$ 100,000	$ 900,000
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition	1 year 0 months 3 days	2 years 5 months 19 days