Income Taxes (Income Tax Reconciliation) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Federal statutory percentage rate	35.00%	35.00%	35.00%
Domestic statutory rate at 35%	$ 28,828,000	$ 21,766,000	$ 23,403,000
Increase (reduction) from:
Jurisdictional rate differences	(1,863,000)	(1,936,000)	(2,192,000)
Valuation allowance	308,000	1,731,000	797,000
Stock based compensation	(778,000)	275,000	257,000
U.S. state taxes	2,463,000	1,295,000	1,942,000
Domestic production deduction	(1,039,000)	(618,000)	(518,000)
R&D credit	(500,000)	(329,000)	(475,000)
Other, net	397,000	(40,000)	444,000
Provision for income taxes before tax reform	27,816,000
Tax Reform:
Rate change of deferreds	(3,334,000)	0	0
Mandatory deemed repatriation expense	13,104,000	0	0
Other	466,000	0	0
Impact of tax reform	10,236,000	0	0
Total income taxes	$ 38,052,000	$ 22,144,000	$ 23,658,000
Effective tax rate	34.00%
Effective tax rate	46.00%	36.00%	35.00%