Share-Based Compensation Plans - Summary of Option Activity (Details) - Non-qualified Stock Options - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Shares
Shares, outstanding, beginning balance	1,338,468
Shares, granted	158,200	133,500	259,600
Shares, exercised	(405,526)
Shares, forfeited	0
Shares, expired	(10,900)
Shares, outstanding, ending balance	1,080,242	1,338,468
Shares, exercisable	788,542
Weighted Average Exercise Price
Weighted average exercise price, outstanding, beginning balance (in dollars per share)	$ 54.08
Weighted average exercise price, granted (in dollars per share)	75.70
Weighted average exercise price, exercised (in dollars per share)	46.00
Weighted average exercise price, forfeited (in dollars per share)	0.00
Weighted average exercise price, expired (in dollars per share)	48.91
Weighted average exercise price, outstanding, ending balance (in dollars per share)	60.33	$ 54.08
Weighted average exercise price, exercisable (in dollars per share)	$ 52.25
Weighted Average Remaining Contractual Term
Weighted average remaining contractual term, outstanding, end of period	6 years 6 months 11 days
Weighted average remaining contractual term, exercisable	5 years 9 months 11 days
Aggregate Intrinsic Value
Aggregate intrinsic value, outstanding, end of period	$ 2,261,513
Aggregate intrinsic value, exercisable, end of period	$ 2,261,513