Leases - Lease cost and other information (Details) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)
Lease Expense Components:
Operating lease expense	$ 2,173	$ 4,319
Short-term lease expense	132	276
Variable lease expense	117	186
Total lease expense	2,422	4,781
Supplemental Cash Flow Information Related to Leases:
Cash paid for amounts included in the measurement of lease liabilities - operating leases	1,918	3,808
ROU assets obtained in exchange for new lease liabilities during first quarter 2019- operating leases	$ 2,994	$ 4,950
Weighted - average remaining lease term (years) - Operating leases	14 years 4 months 24 days	14 years 4 months 24 days
Weighted - average discount rate - Operating leases	4.00%	4.00%
Supplemental Balance Sheet Information Related to Leases
Operating lease ROU assets	$ 84,464	$ 84,464
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Property, Plant and Equipment, Net	Property, Plant and Equipment, Net
Operating lease liabilities	$ 84,968	$ 84,968
Operating Lease, Liability, Statement of Financial Position [Extensible List]	Other Liabilities	Other Liabilities