Summary of Significant Accounting Policies - Restructuring (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 10,505,000	$ 0	$ 0
Office lease terminations and modifications [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	9,200,000
Transition services including severance costs [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1,800,000
Operating lease adjustment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ (500,000)