Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance			$ 2,042,306	$ 1,338,191
Other comprehensive income before reclassifications			28,039	(44,904)
Amounts reclassified from accumulated other comprehensive income (loss)			7,960	(1,398)
Total changes in other comprehensive income (loss)	$ 4,912	$ (3,376)	35,999	(46,302)
Amounts reclassified to accumulated deficit pursuant to adoption of new accounting standard					$ 9,229	$ 0
Ending Balance	2,934,481	1,803,244	2,934,481	1,803,244
Foreign Currency Translation Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance			(21,031)	(7,862)
Other comprehensive income before reclassifications			6,800	(11,137)
Amounts reclassified from accumulated other comprehensive income (loss)			0	0
Total changes in other comprehensive income (loss)			6,800	(11,137)
Ending Balance	(13,282)	(18,999)	(13,282)	(18,999)
Unrealized Holding Gains (Losses), Net of Tax, On Available-For-Sale Debt Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance			(594)	(10)
Other comprehensive income before reclassifications			137	(170)
Amounts reclassified from accumulated other comprehensive income (loss)			0	0
Total changes in other comprehensive income (loss)			137	(170)
Ending Balance	(457)	(180)	(457)	(180)
Unrealized Holding Gains (Losses), Net of Tax, On Equity Securities, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance			25,069	17,531
Other comprehensive income before reclassifications			0	(7,616)
Amounts reclassified from accumulated other comprehensive income (loss)			0	0
Total changes in other comprehensive income (loss)			0	(7,616)
Ending Balance	0	9,915	0	9,915
Unrealized Holding Gains (Losses), Net of Tax, On Foreign Currency Forward Contracts
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance			(15,016)	11,514
Other comprehensive income before reclassifications			21,102	(25,981)
Amounts reclassified from accumulated other comprehensive income (loss)			7,960	(1,398)
Total changes in other comprehensive income (loss)			29,062	(27,379)
Ending Balance	14,046	(15,865)	14,046	(15,865)
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance			(11,572)	21,173
Total changes in other comprehensive income (loss)			35,999	(46,302)
Amounts reclassified to accumulated deficit pursuant to adoption of new accounting standard					$ (24,120)
Ending Balance	307	$ (25,129)	307	$ (25,129)
Accounting Standards Update 2014-09
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified to accumulated deficit pursuant to adoption of new accounting standard	(24,120)		(24,120)
Accounting Standards Update 2014-09 | Foreign Currency Translation Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified to accumulated deficit pursuant to adoption of new accounting standard	949		949
Accounting Standards Update 2014-09 | Unrealized Holding Gains (Losses), Net of Tax, On Available-For-Sale Debt Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified to accumulated deficit pursuant to adoption of new accounting standard	0		0
Accounting Standards Update 2014-09 | Unrealized Holding Gains (Losses), Net of Tax, On Equity Securities, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified to accumulated deficit pursuant to adoption of new accounting standard	(25,069)		(25,069)
Accounting Standards Update 2014-09 | Unrealized Holding Gains (Losses), Net of Tax, On Foreign Currency Forward Contracts
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified to accumulated deficit pursuant to adoption of new accounting standard	$ 0		$ 0