Summary of Significant Accounting Policies - New Accounting Pronouncements (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2019
Summary Of Significant Policies [Line Items]
Loss on extinguishment of debt	$ 2,200	$ 2,209	$ 0	$ 0
Scenario, Forecast | Accounting Standards Update 2016-02 | Minimum
Summary Of Significant Policies [Line Items]
Operating lease, liability					$ 44,000
Operating lease, right-of-use asset					44,000
Scenario, Forecast | Accounting Standards Update 2016-02 | Maximum
Summary Of Significant Policies [Line Items]
Operating lease, liability					49,000
Operating lease, right-of-use asset					$ 49,000