Significant Accounting Policies - Narrative (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Jan. 01, 2020	Dec. 31, 2019	Jun. 30, 2019
Retained earnings	$ 2,249,391		$ 2,141,302	$ 2,049,995
Accounting Standards Update 2016 13 [Member]
Retained earnings		$ (700)