UNAUDITED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Income Statement [Abstract]
Agency revenues	$ 1,199,348	$ 1,041,144
Merchant revenues	494,675	526,998
Advertising and other revenues	146,671	73,660
Total revenues	1,840,694	1,641,802
Cost of revenues	168,458	235,331
Gross profit	1,672,236	1,406,471
Operating expenses:
Advertising — Online	643,216	520,848
Advertising — Offline	63,582	53,474
Sales and marketing	81,944	64,311
Personnel, including stock-based compensation of $54,008 and $38,803, respectively	258,984	194,531
General and administrative	100,178	72,981
Information technology	25,361	23,224
Depreciation and amortization	65,002	38,376
Total operating expenses	1,238,267	967,745
Operating income	433,969	438,726
Other income (expense):
Interest income	11,596	1,041
Interest expense	(33,479)	(17,745)
Foreign currency transactions and other	(4,843)	(5,969)
Total other income (expense)	(26,726)	(22,673)
Earnings before income taxes	407,243	416,053
Income tax expense	73,916	84,835
Net income	$ 333,327	$ 331,218
Net income applicable to common stockholders per basic common share	$ 6.42	$ 6.35
Weighted-average number of basic common shares outstanding	51,909	52,153
Net income applicable to common stockholders per diluted common share	$ 6.36	$ 6.25
Weighted-average number of diluted common shares outstanding	52,406	53,018