Summary of Significant Accounting Principles - Accounting Standards Adopted in 2019 (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, right-of-use asset	$ 22,002		$ 0
Operating lease, liability	$ 22,704
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, right-of-use asset		$ 22,000
Operating lease, liability		$ 22,700