Income Taxes (Income Tax Expense Difference) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Tax expense at Federal statutory income tax rate	$ 46,529	$ 28,798	$ 23,161
International tax rate differential	(9,603)	(2,260)	(4,792)
Foreign source income, net of tax credits (excluding U.S. tax reform)	1,087	1,215	2,449
State tax, net of federal	279	(200)	(416)
Unrecognized tax benefits	2,874	(5,555)	148
U.S. tax reform	13,683	0	0
Equity compensation excess tax deductions	(3,867)	0	0
General business credits	(1,080)	(1,125)	(908)
Acquisition related expenses	0	0	453
Distribution related foreign taxes	2,173	12,433	0
Valuation allowance change (excluding U.S. tax reform)	1,393	171	(1,489)
Other	(1,002)	520	1,247
Total	$ 52,466	$ 33,997	$ 19,853