Summary of Significant Accounting Policies - Adoption of New Accounting Standards (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Operating Lease, Right-of-Use Asset	$ 77,754	$ 80,300	$ 0
Lease liabilities	$ 83,800	$ 86,800