Summary of Significant Accounting Policies - Impact of Adoption of Lease Guidance (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Significant Accounting Policies [Line Items]
Operating Lease Right-of-Use Assets	$ 145,949
Other Assets	46,057		$ 26,935
Accounts Payable, Accrued Expenses and Other Liabilities	20,560		24,657
Operating Lease Liabilities	$ 161,201
Deferred Rent Liability			$ 16,417
Accounting Standards Update 2016-02
Significant Accounting Policies [Line Items]
Operating Lease Right-of-Use Assets		$ 129,479
Other Assets		26,069
Accounts Payable, Accrued Expenses and Other Liabilities		23,467
Operating Lease Liabilities		146,220
Accounting Standards Update 2016-02 | Adjustments
Significant Accounting Policies [Line Items]
Operating Lease Right-of-Use Assets		129,479
Other Assets		(866)
Accounts Payable, Accrued Expenses and Other Liabilities		(1,190)
Operating Lease Liabilities		146,220
Deferred Rent Liability		$ (16,417)