Adoption of New Accounting Standards and Recent Accounting Pronouncements (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other investments	$ 16,508		$ 12,214
Accounting Standards Update 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other investments		$ 2,000