CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total		Common Stock	Treasury Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Balance at Dec. 31, 2014	$ 8,566,694		$ 480	$ (2,737,585)	$ 4,923,196	$ 6,640,505	$ (259,902)
Balance (in shares) at Dec. 31, 2014			61,821,000	(9,888,000)
Increase (Decrease) in Stockholders' Equity
Net income	2,551,360					2,551,360
Foreign currency translation adjustments	(114,505)	[1]					(114,505)
Net unrealized gain (loss) on marketable securities	619,259	[2]					619,259
Reclassification adjustment for convertible debt	329				329
Exercise of stock options and vesting of restricted stock units and performance share units	20,851		$ 2		20,849
Exercise of stock options and vesting of restricted stock units and performance share units (in shares)			219,000
Repurchase of common stock	$ (3,089,055)			$ (3,089,055)
Repurchase of common stock (in shares)	(2,539,921)			(2,540,000)
Stock-based compensation and other stock-based payments	$ 249,133				249,133
Adjustments to Additional Paid in Capital Senior Convertible Notes Converted	(110,105)				(110,105)
Excess tax benefits on stock-based awards and other equity deductions	101,508				101,508
Balance at Dec. 31, 2015	8,795,469		$ 482	$ (5,826,640)	5,184,910	9,191,865	244,852
Balance (in shares) at Dec. 31, 2015			62,040,000	(12,428,000)
Increase (Decrease) in Stockholders' Equity
Net income	2,134,987					2,134,987
Foreign currency translation adjustments	(93,984)	[1]					(93,984)
Net unrealized gain (loss) on marketable securities	(285,552)	[2]					(285,552)
Reclassification adjustment for convertible debt	(28,538)				(28,538)
Exercise of stock options and vesting of restricted stock units and performance share units	15,572		$ 3		15,569
Exercise of stock options and vesting of restricted stock units and performance share units (in shares)			339,000
Repurchase of common stock	$ (1,028,524)			$ (1,028,524)
Repurchase of common stock (in shares)	(762,984)			(763,000)
Stock-based compensation and other stock-based payments	$ 249,726				249,726
Excess tax benefits on stock-based awards and other equity deductions	60,986				60,986
Balance at Dec. 31, 2016	9,820,142		$ 485	$ (6,855,164)	5,482,653	11,326,852	(134,684)
Balance (in shares) at Dec. 31, 2016			62,379,000	(13,191,000)
Increase (Decrease) in Stockholders' Equity
Net income	2,340,765					2,340,765
Foreign currency translation adjustments	295,547	[1]					295,547
Net unrealized gain (loss) on marketable securities	76,119	[2]					76,119
Reclassification adjustment for convertible debt	25,575				25,575
Exercise of stock options and vesting of restricted stock units and performance share units	5,140		$ 1		5,139
Exercise of stock options and vesting of restricted stock units and performance share units (in shares)			160,000
Repurchase of common stock	$ (1,843,665)			$ (1,843,665)
Repurchase of common stock (in shares)	(1,025,890)			(1,026,000)
Stock-based compensation and other stock-based payments	$ 261,274				261,274
Adjustments to Additional Paid in Capital Senior Convertible Notes Converted	(539)				(540)
Conversion of debt (in shares)			150,000
Conversion of debt			$ 1
Balance at Dec. 31, 2017	11,260,598		$ 487	$ (8,698,829)	5,783,089	13,938,869	$ 236,982
Balance (in shares) at Dec. 31, 2017			62,689,000	(14,217,000)
Increase (Decrease) in Stockholders' Equity
Cumulative effect of adoption of accounting standard updates	$ 280,240				$ 8,988	$ 271,252

[1] Foreign currency translation adjustments result from currency fluctuations on the translation of the Company's international non-U.S. Dollar denominated net assets, net of the impact of net investment hedges. Foreign currency translation adjustments were favorable for the year ended December 31, 2017 compared to the year ended December 31, 2016 because the U.S. Dollar weakened against certain currencies in which the Company's net assets are denominated. Foreign currency translation adjustments also include a tax benefit of $174,584 for the year ended December 31, 2017 and tax charges of $34,268 and $60,418 for the years ended December 31, 2016 and 2015, respectively, associated with the Company's Euro-denominated debt, which is designated as a net investment hedge against the impact of currency fluctuations of the Company's Euro-denominated net assets (see Note 12). Prior to the U.S. Tax Cuts and Jobs Act (the "Tax Act"), the remaining balance in foreign currency translation adjustments excluded U.S. federal and state income taxes as a result of the Company's intention to indefinitely reinvest the earnings of its international subsidiaries outside of the United States. In accordance with the Tax Act, generally future repatriation of the Company's international cash will not be subject to a U.S. federal income tax liability as a dividend, but will be subject to U.S. state income taxes and international withholding taxes.

[2] Net of tax charges of $81,166, $15,313 and $1,551 for the years ended December 31, 2017, 2016 and 2015, respectively. For the year ended December 31, 2017, the Company recorded a U.S. deferred tax liability of $63,353 related to net cumulative unrealized gains associated with certain international investments, which will be subject to U.S. federal and state income taxes if the gains are realized. Net unrealized gain (loss) on marketable securities includes net unrealized gains of $86,019 for the year ended December 31, 2017, net unrealized losses of $332,756 for the year ended December 31, 2016, and net unrealized gains of $615,848 for the year ended December 31, 2015, related to the Company's investments in Ctrip.com International Ltd. ("Ctrip"), which are exempt from tax in the Netherlands.