Share-based Compensation (Nonvested Restricted Stock) (Details) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) Installment $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares
Nonvested Awards, Weighted Average Grant Date Fair Value [Roll Forward]
Common shares reserved for stock option and restricted stock grants	5,312,000.000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting rate, initial year (percent)	33.33%
Quarterly award vesting installments after initial year | Installment	8
Nonvested Awards, Number of Shares [Roll Forward]
Nonvested awards, Shares, beginning balance	107,095	123,654	203,314
Nonvested awards, Shares Granted	5,623	56,251	26,119
Nonvested awards, Shares Vested	(68,788)	(72,810)	(101,441)
Nonvested awards, Shares Forfeited	(3,514)	0	(4,338)
Nonvested awards, Shares, ending balance	40,416	107,095	123,654
Nonvested Awards, Weighted Average Grant Date Fair Value [Roll Forward]
Nonvested awards outstanding, Weighted Average Grant Date Fair Value, beginning balance (in dollars per share) | $ / shares	$ 45.74	$ 31.17	$ 25.56
Nonvested awards, Granted, Weighted Average Grant Date Fair Value (in dollars per share) | $ / shares	76.47	56.75	44.79
Nonvested awards, Vested, Weighted Average Grant Date Fair Value (in dollars per share) | $ / shares	40.67	29.50	23.25
Nonvested awards, Forfeited, Weighted Average Grant Date Fair Value (in dollars per share) | $ / shares	46.24	0.00	35.54
Nonvested awards outstanding, Weighted Average Grant Date Fair Value, ending balance (in dollars per share) | $ / shares	$ 58.60	$ 45.74	$ 31.17
Unrecognized compensation cost, share-based compensation arrangements | $	$ 2.1
Weighted average period to recognize nonvested awards (in years)	1 year 8 months 26 days
Fair value of shares vested during period | $	$ 2.8	$ 2.1	$ 2.4
Stock compensation expense recognized on restricted grants | $	$ 2.4	$ 2.4	$ 2.5