Unaudited Condensed Consolidated Statement of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Unaudited Condensed Consolidated Statement of Comprehensive Income [Abstract]
Net income	$ 103,281	$ 68,562	$ 185,329	$ 243,311
Other comprehensive income:
Foreign currency translation adjustments	(5,909)	10,441	(15,501)	13,605
Total comprehensive income	97,372	79,003	169,828	256,916
Total comprehensive income attributable to noncontrolling interests	(41)	(88)	(98)	(135)
Total comprehensive income attributable to common stockholders	$ 97,331	$ 78,915	$ 169,730	$ 256,781