Segment Information Gross Profit by Segment and Category (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Gross Profit by Category [Line Items]
Sales Revenue, Services, Net									$ 1,266,452	$ 1,206,441	$ 1,250,149
Gross profit	$ 386,918	$ 309,425	$ 328,067	$ 309,451	$ 351,906	$ 293,268	$ 315,377	$ 320,102	1,333,861	1,280,653	1,287,810
North America [Member]
Gross Profit by Category [Line Items]
Sales Revenue, Services, Net									1,914,168	2,151,769	2,047,742
Gross profit									927,678	885,547	801,571
International [Member]
Gross Profit by Category [Line Items]
Gross profit									406,183	395,106	486,239
Local [Member] | North America [Member]
Gross Profit by Category [Line Items]
Sales Revenue, Services, Net									825,579	762,314	701,312
Gross profit									708,573	660,983	600,893
Local [Member] | International [Member]
Gross Profit by Category [Line Items]
Sales Revenue, Services, Net									281,466	270,045	335,112
Gross profit									265,348	250,435	310,842
Travel [Member] | North America [Member]
Gross Profit by Category [Line Items]
Sales Revenue, Services, Net									78,495	82,577	81,731
Gross profit									60,594	64,355	67,027
Travel [Member] | International [Member]
Gross Profit by Category [Line Items]
Sales Revenue, Services, Net									43,786	49,756	59,482
Gross profit									40,288	45,191	52,220
Third party and other [Member] | Goods [Member] | North America [Member]
Gross Profit by Category [Line Items]
Sales Revenue, Services, Net									16,768	9,068	7,151
Gross profit									12,929	7,470	5,931
Third party and other [Member] | Goods [Member] | International [Member]
Gross Profit by Category [Line Items]
Sales Revenue, Services, Net									20,358	32,681	65,361
Gross profit									17,910	27,976	55,141
Direct [Member] | Goods [Member] | North America [Member]
Gross Profit by Category [Line Items]
Gross profit									145,582	152,739	127,720
Direct [Member] | Goods [Member] | International [Member]
Gross Profit by Category [Line Items]
Gross profit									$ 82,637	$ 71,504	$ 68,036