Summary of Significant Accounting Policies Summary of Significant Accounting Policies - Restructuring (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 9,076,000	$ 0	$ 0
Restructuring cost expected to be incurred	1,800,000
Office lease terminations and modifications [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	8,300,000
Transition services including severance costs [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1,100,000
Operating lease adjustment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 300,000