Leases - Maturities of lease liabilities under non-cancellable leases (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Jan. 01, 2019
Rent Payments
Remainder of 2019	$ 2,146
2020	8,753
2021	9,007
2022	9,001
2023	9,173
Thereafter	43,686
Total lease payments	81,766
Less: imputed interest	19,529
Present value of lease liabilities	62,237	$ 65,800
Sublease Receipts
2019	288
2020	888
2021	775
2022	804
2023	822
Thereafter	1,382
Sublease Receipts	4,959
Total Cash Outflows
2019	1,858
2020	7,865
2021	8,232
2022	8,197
2023	8,351
Thereafter	42,304
Total Cash Outflows	$ 76,807