Summary of Significant Accounting Policies (Tax Effects of Componenets of Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Summary of Significant Accounting Policies [Abstract]
Defined benefit pension plan adjustments, Before-Tax Amount	$ (4,452)	$ 31	$ (13,887)
Defined benefit pension plan adjustments, Tax (Expense) Benefit	1,829	1,995	5,732
Defined benefit pension plan adjustments, Net-of-Tax Amount	(2,623)	2,026	(8,155)
Foreign currency translation adjustment, Before-Tax Amount	(439)	(5,897)	(1,086)
Foreign currency translation adjustment, Tax (Expense) Benefit	178	2,683	448
Foreign currency translation adjustment, Net-of-Tax Amount	(261)	(3,214)	(638)
Unrealized gain (loss) in fair value of investments, Before-Tax Amount	(576)	1,123	346
Unrealized gain (loss) in fair value of investments, Tax (Expense) Benefit	236	(357)	(141)
Unrealized gain (loss) in fair value of investments, Net-of-Tax Amount	(340)	766	205
Unrealized gain (loss) in fair value of interest rate swap, Before-Tax Amount	(45)	(37)	594
Unrealized gain (loss) in fair value of interest rate swap, Tax (Expense) Benefit	21	(88)	(245)
Unrealized gain (loss) in fair value of interest rate swap, Net-of-Tax Amount	(24)	(125)	349
Total other comprehensive (loss) income, Before-Tax Amount	(5,512)	(4,780)	(14,033)
Total other comprehensive (loss) income, Tax (Expense) Benefit	2,264	4,233	5,794
Total other comprehensive loss, net of tax	$ (3,248)	$ (547)	$ (8,239)