Condensed Consolidated Statements of Stockholders Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Other Comprehensive Income (Loss)	Accumulated Deficit​
Beginning Balance at Dec. 31, 2018	$ 680,941	$ 1,232	$ 1,716,894	$ (1,422)	$ (1,035,763)
Balance (in shares) at Dec. 31, 2018		123,192,540
Increase (Decrease) in Stockholders' Equity
Equity component of convertible notes, net of tax and issuance costs	268,390		268,390
Shares issued to settle convertible notes (in shares)		2,158,991
Shares issued to settle convertible notes	182,435	$ 22	182,413
Settlement of convertible notes, net of tax	(300,768)		(300,768)
Exercise of common stock options	3,650	$ 2	3,648
Exercise of common stock options (in shares)		235,278
Issuance of common stock to fund the Company's 401(k) match	7,409	$ 1	7,408
Issuance of common stock to fund the Company's 401(k) match (in shares)		86,532
Compensation expense related to issuance of stock options and restricted stock awards	16,166	$ 35	16,131
Compensation expense related to issuance of stock options and restricted stock awards (in shares)		3,410,481
Net loss	(82,939)				(82,939)
Accumulated other comprehensive income	1,656			1,656
Ending Balance at Mar. 31, 2019	776,940	$ 1,292	1,894,116	234	(1,118,702)
Balance (in shares) at Mar. 31, 2019		129,083,822
Beginning Balance at Dec. 31, 2018	$ 680,941	$ 1,232	1,716,894	(1,422)	(1,035,763)
Balance (in shares) at Dec. 31, 2018		123,192,540
Increase (Decrease) in Stockholders' Equity
Shares issued to settle convertible notes (in shares)	2,159,017
Issuance of common stock for business combinations	$ 0
Net loss	(161,966)
Ending Balance at Sep. 30, 2019	748,284	$ 1,299	1,945,046	(332)	(1,197,729)
Balance (in shares) at Sep. 30, 2019		129,817,885
Beginning Balance at Mar. 31, 2019	776,940	$ 1,292	1,894,116	234	(1,118,702)
Balance (in shares) at Mar. 31, 2019		129,083,822
Increase (Decrease) in Stockholders' Equity
Equity component of convertible notes, net of tax and issuance costs	(22)		(22)
Exercise of common stock options	1,348	$ 1	1,347
Exercise of common stock options (in shares)		78,793
Compensation expense related to issuance of stock options and restricted stock awards	20,143	$ 1	20,142
Compensation expense related to issuance of stock options and restricted stock awards (in shares)		104,845
Purchase of employee stock purchase plan shares	4,137	$ 1	4,136
Purchase of employee stock purchase plan shares (in shares)		93,588
Net loss	(38,502)				(38,502)
Accumulated other comprehensive income	1,488			1,488
Ending Balance at Jun. 30, 2019	765,532	$ 1,295	1,919,719	1,722	(1,157,204)
Balance (in shares) at Jun. 30, 2019		129,361,048
Increase (Decrease) in Stockholders' Equity
Settlement of convertible notes, net of tax	$ 1		1
Settlement of convertible notes (in shares)	26
Exercise of common stock options	$ 1,391	$ 2	1,389
Exercise of common stock options (in shares)		178,628
Compensation expense related to issuance of stock options and restricted stock awards	24,348	$ 2	24,346
Compensation expense related to issuance of stock options and restricted stock awards (in shares)		278,180
Purchase of employee stock purchase plan shares	0
Purchase of employee stock purchase plan shares (in shares)		3
Issuance costs	(409)
Net loss	(40,525)				(40,525)
Accumulated other comprehensive income	(2,054)			(2,054)
Ending Balance at Sep. 30, 2019	748,284	$ 1,299	1,945,046	(332)	(1,197,729)
Balance (in shares) at Sep. 30, 2019		129,817,885
Beginning Balance at Dec. 31, 2019	$ 2,288,061	$ 1,477	3,406,440	(100)	(1,119,756)
Balance (in shares) at Dec. 31, 2019	147,625,696	147,625,696
Increase (Decrease) in Stockholders' Equity
Equity component of convertible notes, net of tax and issuance costs	$ 346,641		346,641
Settlement of convertible notes, net of tax	(64,199)		(64,199)
Exercise of common stock options	4,300	$ 2	4,298
Exercise of common stock options (in shares)		160,286
Issuance of common stock to fund the Company's 401(k) match	12,007	$ 1	12,006
Issuance of common stock to fund the Company's 401(k) match (in shares)		136,559
Compensation expense related to issuance of stock options and restricted stock awards	29,560	$ 11	29,549
Compensation expense related to issuance of stock options and restricted stock awards (in shares)		1,141,376
Issuance of common stock for business combinations	28,597	$ 4	28,593
Issuance of common stock for business combinations (in shares)		382,947
Net loss	(105,697)				(105,697)
Accumulated other comprehensive income	(1,617)			(1,617)
Ending Balance at Mar. 31, 2020	2,537,653	$ 1,495	3,763,328	(1,717)	(1,225,453)
Balance (in shares) at Mar. 31, 2020		149,446,864
Beginning Balance at Dec. 31, 2019	$ 2,288,061	$ 1,477	3,406,440	(100)	(1,119,756)
Balance (in shares) at Dec. 31, 2019	147,625,696	147,625,696
Increase (Decrease) in Stockholders' Equity
Issuance of common stock for business combinations	$ 28,847
Issuance of common stock for business combinations (in shares)	386,293
Net loss	$ (411,723)
Ending Balance at Sep. 30, 2020	$ 2,337,100	$ 1,505	3,865,990	1,084	(1,531,479)
Balance (in shares) at Sep. 30, 2020	150,373,486	150,373,486
Beginning Balance at Mar. 31, 2020	$ 2,537,653	$ 1,495	3,763,328	(1,717)	(1,225,453)
Balance (in shares) at Mar. 31, 2020		149,446,864
Increase (Decrease) in Stockholders' Equity
Exercise of common stock options	6,638	$ 2	6,636
Exercise of common stock options (in shares)		208,434
Compensation expense related to issuance of stock options and restricted stock awards	40,039	$ 2	40,037
Compensation expense related to issuance of stock options and restricted stock awards (in shares)		157,579
Purchase of employee stock purchase plan shares	9,799	$ 2	9,797
Purchase of employee stock purchase plan shares (in shares)		167,921
Net loss	(86,142)				(86,142)
Accumulated other comprehensive income	3,206			3,206
Ending Balance at Jun. 30, 2020	2,511,193	$ 1,501	3,819,798	1,489	(1,311,595)
Balance (in shares) at Jun. 30, 2020		149,980,798
Increase (Decrease) in Stockholders' Equity
Exercise of common stock options	4,470	$ 1	4,469
Exercise of common stock options (in shares)		140,145
Compensation expense related to issuance of stock options and restricted stock awards	41,476	$ 2	41,474
Compensation expense related to issuance of stock options and restricted stock awards (in shares)		249,197
Issuance of common stock for business combinations	250	$ 1	249
Issuance of common stock for business combinations (in shares)		3,346
Net loss	(219,884)				(219,884)
Accumulated other comprehensive income	(405)			(405)
Ending Balance at Sep. 30, 2020	$ 2,337,100	$ 1,505	$ 3,865,990	$ 1,084	$ (1,531,479)
Balance (in shares) at Sep. 30, 2020	150,373,486	150,373,486