Stock-Based Compensation (Summary of Restricted Share and Performance Share Activity) (Details) - Restricted Stock	3 Months Ended
	Mar. 31, 2018 $ / shares shares
Time-Based
Number of Shares
Outstanding - beginning of year (in shares) | shares	342,859
Granted (in shares) | shares	16,500
Vested (in shares) | shares	(14,667)
Canceled or expired (in shares) | shares	(4,500)
Outstanding - end of year (in shares) | shares	340,192
Weighted Average Grant Date Fair Value
Outstanding - beginning of year (in dollars per share) | $ / shares	$ 34.71
Granted (in dollars per share) | $ / shares	43.74
Vested (in dollars per share) | $ / shares	37.76
Canceled or expired (in dollars per share) | $ / shares	37.50
Outstanding - end of year (in dollars per share) | $ / shares	$ 34.71
Performance-Based
Number of Shares
Outstanding - beginning of year (in shares) | shares	165,000
Granted (in shares) | shares	0
Vested (in shares) | shares	0
Canceled or expired (in shares) | shares	0
Outstanding - end of year (in shares) | shares	165,000
Weighted Average Grant Date Fair Value
Outstanding - beginning of year (in dollars per share) | $ / shares	$ 38.10
Granted (in dollars per share) | $ / shares	0.00
Vested (in dollars per share) | $ / shares	0.00
Canceled or expired (in dollars per share) | $ / shares	0.00
Outstanding - end of year (in dollars per share) | $ / shares	$ 38.10