Share-Based Compensation Plans - Summary of Non-qualified Option Activity (Details) - Non-qualified Stock Options	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares
Shares
Outstanding, beginning balance (in shares) | shares	1,174,200
Granted (in shares) | shares	153,700
Exercised (in shares) | shares	(158,700)
Forfeited (in shares) | shares	(40,000)
Expired (in shares) | shares	0
Outstanding, ending balance (in shares) | shares	1,129,200
Exercisable (in shares) | shares	691,100
Weighted Average Exercise Price
Weighted average exercise price, outstanding, beginning balance (in dollars per share) | $ / shares	$ 60.99
Weighted average exercise price, granted (in dollars per share) | $ / shares	63.97
Weighted average exercise price, exercised (in dollars per share) | $ / shares	44.84
Weighted average exercise price, forfeited (in dollars per share) | $ / shares	67.91
Weighted average exercise price, expired (in dollars per share) | $ / shares	0.00
Weighted average exercise price, outstanding, ending balance (in dollars per share) | $ / shares	63.42
Weighted average exercise price, exercisable (in dollars per share) | $ / shares	$ 63.92
Weighted Average Remaining Contractual Term
Weighted average remaining contractual term, outstanding	6 years 3 months
Weighted average remaining contractual term, exercisable	5 years 1 month
Aggregate Intrinsic Value
Aggregate intrinsic value, outstanding, end of period | $	$ 1,428,439
Aggregate intrinsic value, exercisable, end of period | $	$ 668,266