Property and equipment, net - Lease and maturity of lease liabilities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Lease liabilities
Lessee, Operating Lease, Existence of Residual Value Guarantee [true false]	false
Lessee, Operating Lease, Existence of Option to Extend [true false]	true
Operating lease liabilities, current	$ 9,021		$ 9,343
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Accrued Liabilities, Current		Accrued Liabilities, Current
Finance lease liabilities, current	$ 910		$ 664	[1]
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	Finance lease liabilities, current		Finance lease liabilities, current
Operating lease liabilities, noncurrent	$ 11,151		$ 11,854
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Other Liabilities, Noncurrent		Other Liabilities, Noncurrent
Finance lease liabilities, noncurrent	$ 31,959		$ 31,918	[1]
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Finance lease liabilities, noncurrent		Finance lease liabilities, noncurrent
Total lease liabilities	$ 53,041		$ 53,779
Cash paid for operating lease liabilities	3,200	$ 2,800
Cash paid for financing lease liabilities in operating cash flows	200	200
Cash paid for financing lease liabilities in financing cash flows	$ 187	195
Maturity of our finance lease liabilities
Weighted average lease term, finance leases	15 years 4 months 24 days
Weighted average lease term, operating leases	3 years 1 month 6 days
Weighted average discount rate, operating leases	3.60%
Weighted average discount rate, finance leases	4.40%
Expense related to our operating leases	$ 3,200	3,600
Amortization on our finance lease right-of-use assets	600	200
Interest expense on finance lease liabilities	300
Rent expense	$ 3,500	$ 3,300

[1] The condensed consolidated balance sheet at December 31, 2019 has been derived from the audited consolidated financial statements at that date.