Significant Accounting Policies Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2019	Sep. 30, 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			$ 299,500	$ 170,500
Operating Lease, Liability			$ 325,300	$ 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					$ (14,672)	$ (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					(14,672)	$ (2,285)
Previously reported cumulative effect reduction to retained earnings					(12,600)
Retroactive adjustment to cumulative effect for new accounting principle					$ (2,100)
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