Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 121,677	$ 91,769	$ 261,515	$ 180,506
Other comprehensive (loss) gain, net of tax:
Foreign currency translation adjustments	(10,203)	7,222	(6,826)	9,710
Unrealized gain (loss) on investments:
Unrealized gains (losses) during the period, net of income taxes of $(52), $(51), $372 and $(32)	32	165	(1,325)	141
Less: reclassification adjustment for losses (gains) realized in net income, net of income taxes of $(31), $(53), $(46) and $(43)	112	111	(162)	89
Unrealized gain (loss) on investments:	144	276	(1,487)	230
Total other comprehensive (loss) gain, net of tax	(10,059)	7,498	(8,313)	9,940
Comprehensive income	$ 111,618	$ 99,267	$ 253,202	$ 190,446

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income. Excludes changes in equity resulting from investments by owners and distributions to owners.

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