Consolidated Statements of Stockholders' Equity (Parenthetical) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash dividend declared	$ 0.60	$ 0.57	$ 0.46
Retained Earnings [Member]
Cash dividend declared	$ 0.60	$ 0.57	$ 0.46
Accumulated Other Comprehensive Income (Loss) [Member]
Minimum Pension adjustment, tax expense	$ 111,000	$ 449,000	$ 478,000
Tax expense for foreign currency	0	$ 658,000	$ 203,000
Tax expense for interest rate swap	$ 52,000