Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 128,319	$ 101,739	$ 389,834	$ 282,245
Other comprehensive (loss) gain, net of tax:
Foreign currency translation adjustments	(435)	7,318	(7,261)	17,028
Unrealized (loss) gain on investments:
Unrealized (losses) gains during the period, net of income taxes of $91, $(116), $463 and $(148)	(337)	294	(1,662)	435
Less: reclassification adjustment for losses (gains) realized in net income, net of income taxes of $(29), $(41), $(75) and $(84)	130	105	(32)	194
Unrealized (loss) gain on investments:	(207)	399	(1,694)	629
Total other comprehensive (loss) gain, net of tax	(642)	7,717	(8,955)	17,657
Comprehensive income	$ 127,677	$ 109,456	$ 380,879	$ 299,902

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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