Summary of Significant Accounting Policies - Adoption of New Accounting Standards (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Operating lease, right-of-use asset	$ 95,388	$ 80,300	$ 0
Lease liabilities	$ 100,684	$ 86,800