Share-Based Compensation Plans - Company's stock option activity (Details) - Employee Stock Option [Member] $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2019 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Outstanding at beginning of year | shares	1,173,620
Shares, Granted | shares	2,500
Shares, Exercised | shares	(18,795)
Shares, Forfeited or expired | shares	(2,750)
Shares, Outstanding at end of year | shares	1,154,575
Shares, Exercisable at end of year | shares	673,092
Weighted Average Exercise Price, Outstanding at beginning of year (in dollars per share) | $ / shares	$ 27.96
Weighted Average Exercise Price, Granted (in dollars per share) | $ / shares	28.77
Weighted Average Exercise Price, Exercised (in dollars per share) | $ / shares	27.75
Weighted Average Exercise Price, Forfeited or expired (in dollars per share) | $ / shares	31.94
Weighted Average Exercise Price, Outstanding at end of year (in dollars per share) | $ / shares	27.95
Weighted Average Exercise Price, Exercisable at end of year (in dollars per share) | $ / shares	$ 26.89
Weighted Average Remaining Contractual Life (Years), Outstanding - December 31, 2018	3 years 8 months 12 days
Weighted Average Remaining Contractual Life (Years), Exercisable - December 31, 2018	1 year 10 months 24 days
Aggregate Intrinsic Value, Outstanding at December 31, 2018 | $	$ 505,000
Aggregate Intrinsic Value, Exercisable at December 31, 2018 | $	$ 284,000