Leases (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) ft²	Jun. 30, 2019 USD ($)	Dec. 31, 2019
Lease terms
Option to extend			20 years
Weighted-average remaining lease term	9 years		9 years		9 years
Weighted average discount rate - Operating leases	4.90%		4.90%		4.90%
Increase in Right-of-Use Asset			$ 7,935,000
Increase in operating lease liability			7,000,000
Lease expense
Operating lease expense	$ 6,944,000	$ 6,397,000	13,806,000	$ 12,793,000
Variable lease expense	2,051,000	1,336,000	3,588,000	2,628,000
Rent expense	$ 8,995,000	$ 7,733,000	$ 17,394,000	$ 15,421,000
Minimum
Lease terms
Remaining lease terms	1 year		1 year
Maximum
Lease terms
Remaining lease terms	15 years		15 years
DC2 Washington DC
Lease terms
Net Leased Space | ft²			25,000
Increase in Right-of-Use Asset			$ 7,000,000.0