Significant Accounting Policies Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Lease, Right-of-Use Asset	$ 284,500		$ 170,500
Operating Lease, Liability	291,700		$ 174,400
Recognition of right of use asset related to the new corporate headquarters facility	121,700
Recognition of operating lease liability related to the new corporate headquarters facility	$ 121,700
Cumulative effect of new accounting principle in period of adoption				$ (12,611)	$ (2,285)
Retained Earnings [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption				$ (12,611)	$ (2,285)
Two Thousand And Nineteen [Member] | Scenario, Forecast [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Additional premium amortization expense on securities		$ 5,200