CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Comprehensive Income [Abstract]
Net income	$ 477,186us-gaap_ProfitLoss	$ 454,889us-gaap_ProfitLoss	$ 361,775us-gaap_ProfitLoss
Other comprehensive (loss) income:
Foreign currency translation	(17,153)	(5,422)	2,375
Change in unrealized gain on marketable debt securities	7,001	(1,023)	(1,296)
Other	3,614	2,750	213
Total other comprehensive (loss) income	(6,538)	(3,695)	1,292
Comprehensive income	470,648	451,194	363,067
Comprehensive income (loss) attributable to noncontrolling interest	1,419	1,380	(1,025)
Comprehensive income attributable to common stockholders	$ 469,229us-gaap_ComprehensiveIncomeNetOfTax	$ 449,814us-gaap_ComprehensiveIncomeNetOfTax	$ 364,092us-gaap_ComprehensiveIncomeNetOfTax

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

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Amount after tax, before reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature.

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Amount after tax and reclassification adjustments of other comprehensive income (loss).

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The change in other comprehensive income during the reporting period, net of tax, for an item that is not separately disclosed.

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Amount after tax, before reclassification adjustments, of unrealized holding gain (loss) on available-for-sale securities.

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The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest.

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