Consolidated Statement Of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Consolidated Statements of Comprehensive Income [Abstract]
Net income	$ 50,614	$ 30,723	$ 28,479	$ 18,871	$ 49,871	$ 32,358	$ 31,376	$ 25,820	$ 128,687	$ 139,425	$ 152,439
Other comprehensive (loss) income, net of tax:
Foreign currency translation adjustment									(15,471)	25,559	(23,076)
Change in fair value on available-for-sale investments, net of tax (benefit) expense of ($460), zero and $1,495 for the years ended 2018, 2017 and 2016, respectively									(1,418)	0	(2,449)
Other comprehensive (loss) income, net of tax									(16,889)	25,559	(25,525)
Comprehensive income									$ 111,798	$ 164,984	$ 126,914