Accounting Standards and Significant Accounting Policies - Schedule of new accounting pronouncements (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 assets	$ 20,067
Short-term lease liability	(5,777)
Long-term lease liability	(18,956)
Retained earnings	$ (798,157)		$ (771,925)
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use assets		$ 15,633
Short-term lease liability		(4,344)
Long-term lease liability		(12,405)
Retained earnings		$ (1,116)