Common Stock and Treasury Stock (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Common Stock [Line Items]
Share repurchase program, authorized amount	$ 75,800,000		$ 75,800,000
Stock repurchase program, remaining authorization amount	$ 20,100,000		$ 20,100,000
Stock Buy back Program [Member]
Common Stock [Line Items]
Stock Repurchased During Period, Shares	8,600	12,000	11,100	14,500
Stock Repurchased During Period, Value	$ 247,000	$ 454,000	$ 327,000	$ 547,000