Share-Based Payments (Summary of Stock Option Activity) (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Share-Based Payments [Abstract]
Outstanding beginning balance, Common shares under option	4,459,744
Granted, Common shares under option	914,967
Exercised, Common shares under option	(1,154,541)
Forfeited, Common shares under option	(77,644)
Expired, Common shares under option	(1,302)
Outstanding ending balance, Common shares under option	4,141,224	4,459,744
Exercisable, Common shares under option	2,107,984
Outstanding beginning balance, Weighted average exercise price (per share)	$ 24.29
Granted, Weighted average exercise price (per share)	32.12
Exercised, Weighted average exercise price (per share)	23.45
Forfeited, Weighted average exercise price (per share)	27.04
Expired, Weighted average exercise price (per share)	25.76
Outstanding ending balance, Weighted average exercise price (per share)	26.20	$ 24.29
Exercisable, Weighted average exercise price (per share)	$ 24.08
Outstanding, Weighted average remaining contractual life (in years)	7 years 4 months 24 days	7 years 6 months
Exercisable, Weighted average remaining contractual life (in years)	6 years 4 months 24 days
Outstanding beginning balance, Aggregate intrinsic value	$ 17,649
Exercised, Aggregate intrinsic value	13,472
Outstanding ending balance, Aggregate intrinsic value	41,122	$ 17,649
Exercisable, Aggregate intrinsic value	$ 25,401