Stock-Based Compensation - Share Option Activity (Details) (Stock Options [Member], USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2013	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)	(45,450)
Forfeited or expired (in shares)	(56,250)
Outstanding (in shares)	145,950	247,650
Exercisable (in shares)	61,450
Vested or expected to vest (in shares)	143,817
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)	$ 9.87
Forfeited or expired, weighted-average exercise price (in dollars per share)	$ 12.15
Outstanding, weighted-average exercise price (in dollars per share)	$ 8.52	$ 9.59
Exercisable, weighted-average exercise price (in dollars per share)	$ 7.99
Vested or expected to vest, weighted-average exercise price (in dollars per share)	$ 8.51
Outstanding, average remaining contractual term (in years)	7 years 6 months	8 years
Exercisable, average remaining contractual term (in years)	7 years 4 months 24 days
Vested or expected to vest, average remaining contractual term	7 years 6 months
Outstanding, aggregate intrinsic value	$ 2,457,000	$ 2,015,000
Exercisable, aggregate intrinsic value	1,067,000
Vested or expected to vest, aggregate intrinsic value	2,423,000
Total instrinsic value of share options exercised	$ 700,000