Income Taxes - Effective Income Tax Rate Reconciliation (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Tax expense at U.S. federal statutory rates	$ 53,061	$ 49,192	$ 43,003
Increase (decrease) resulting from:
State income taxes, net of federal benefit	857	1,126	723
Foreign tax benefit	(25,263)	(26,181)	(20,515)
Research and experimentation benefit	(5,966)	(758)	(2,908)
Foreign tax credit benefit	(2,152)	(2,738)	(4,465)
Tax audit settlements and lapses of statutes of limitations	(70)	(439)	(509)
Stock compensation	2,658	2,134	1,683
Non-deductible items	2,132	3,100	1,597
Other	(328)	192	619
Total income tax expense	$ 24,929	$ 25,628	$ 19,228