COLLABORATION AND OTHER AGREEMENTS - Schedule of Total Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Collaborative Arrangements and Non-collaborative Arrangements [Line Items]
Revenue	$ 64,677	$ 66,367	$ 204,136	$ 138,331
Asahi Kasei
Collaborative Arrangements and Non-collaborative Arrangements [Line Items]
Revenue	0	0
Product royalties
Collaborative Arrangements and Non-collaborative Arrangements [Line Items]
Revenue	937	0	1,261	0
Product royalties | Pierre Fabre
Collaborative Arrangements and Non-collaborative Arrangements [Line Items]
Revenue	835	0	1,159	0
Product royalties | Ono
Collaborative Arrangements and Non-collaborative Arrangements [Line Items]
Revenue	102	0	102	0
Collaboration and other revenue
Collaborative Arrangements and Non-collaborative Arrangements [Line Items]
Revenue	12,765	10,113	31,323	26,629
Collaboration and other revenue | Pierre Fabre
Collaborative Arrangements and Non-collaborative Arrangements [Line Items]
Revenue	10,704	5,347	22,160	12,370
Collaboration and other revenue | Loxo
Collaborative Arrangements and Non-collaborative Arrangements [Line Items]
Revenue	0	2,416	2,403	7,069
Collaboration and other revenue | Mirati
Collaborative Arrangements and Non-collaborative Arrangements [Line Items]
Revenue	1,500	1,376	3,710	4,187
Collaboration and other revenue | Other partners
Collaborative Arrangements and Non-collaborative Arrangements [Line Items]
Revenue	561	974	3,050	3,003
License and milestone revenue
Collaborative Arrangements and Non-collaborative Arrangements [Line Items]
Revenue	6,728	31,503	69,798	46,364
License and milestone revenue | Pierre Fabre
Collaborative Arrangements and Non-collaborative Arrangements [Line Items]
Revenue	750	750	17,250	2,250
License and milestone revenue | Ono
Collaborative Arrangements and Non-collaborative Arrangements [Line Items]
Revenue	4,596	4,665	6,433	6,502
License and milestone revenue | Loxo
Collaborative Arrangements and Non-collaborative Arrangements [Line Items]
Revenue	0	0	44,000	1,107
License and milestone revenue | Other partners
Collaborative Arrangements and Non-collaborative Arrangements [Line Items]
Revenue	1,382	3,088	2,115	3,505
License and milestone revenue | ASLAN
Collaborative Arrangements and Non-collaborative Arrangements [Line Items]
Revenue	0	23,000	0	23,000
License and milestone revenue | Asahi Kasei
Collaborative Arrangements and Non-collaborative Arrangements [Line Items]
Revenue			0	10,000
Collaboration and license revenue
Collaborative Arrangements and Non-collaborative Arrangements [Line Items]
Revenue	19,493	41,616	101,121	72,993
Reimbursement revenue
Collaborative Arrangements and Non-collaborative Arrangements [Line Items]
Revenue	$ 9,169	$ 24,751	$ 29,970	$ 65,338