Condensed 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	$ 168,524	$ 133,722	$ 157,793	$ 319,368
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments	(379)	343	(1,193)	500
Net change in unrealized gains (losses) on available-for-sale securities	488	(165)	(1,311)	(100)
Other comprehensive income (loss)	109	178	(2,504)	400
Comprehensive income	$ 168,633	$ 133,900	$ 155,289	$ 319,768

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

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