Unaudited Condensed Consolidated Statement of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Unaudited Condensed Consolidated Statement of Comprehensive Income [Abstract]
Net income	$ 68,993	$ 56,141	$ 254,322	$ 299,452
Other comprehensive income:
Foreign currency translation adjustments	5,951	16,580	(9,550)	30,185
Total comprehensive income	74,944	72,721	244,772	329,637
Total comprehensive income attributable to noncontrolling interests	(59)	14	(157)	(121)
Total comprehensive income attributable to common stockholders	$ 74,885	$ 72,735	$ 244,615	$ 329,516