CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 169,300	$ 152,968	$ 249,398	$ 352,116	$ 1,361,112
Other comprehensive income (loss):
Foreign currency translation	(15,246)	8,286	(3,043)	12,368
Unrealized gain (loss) on marketable debt securities	12,857	(62)	12,685	(185)
Other	6,002	398	14,617	316
Total other comprehensive income	3,613	8,622	24,259	12,499	$ 22,414
Comprehensive income	172,913	161,590	273,657	364,615
Comprehensive income attributable to noncontrolling interests	2,781	1,137	4,176	2,158
Comprehensive income attributable to common stockholders	$ 170,132	$ 160,453	$ 269,481	$ 362,457