Income Taxes - Effective Income Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Tax expense at U.S. federal statutory rates	$ 51,727	$ 44,425	$ 53,061
Increase (decrease) resulting from:
State income taxes, net of federal benefit	774	861	857
Foreign tax benefit	(28,602)	(22,307)	(25,263)
Research and experimentation benefit	(2,675)	(2,785)	(5,966)
Foreign tax credit benefit	(3,203)	(1,490)	(2,152)
Lapse of a statute of limitation	(6,170)	(2,869)	(70)
Stock compensation	3,185	2,940	2,658
Non-deductible items	3,442	3,524	2,132
Goodwill impairment	5,775	0	0
Release of valuation allowance	0	(454)	0
Other	(470)	21	(328)
Total income tax expense	$ 23,783	$ 21,866	$ 24,929