Accounting Standards and Significant Accounting Policies - Schedule of new accounting pronouncements (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use assets	$ 20,349		$ 0
Operating lease liabilities	(6,039)		0
Operating lease liabilities, long-term	(18,769)		0
Retained earnings	$ (830,156)		$ (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
Operating lease liabilities		(4,344)
Operating lease liabilities, long-term		(12,405)
Retained earnings		$ (1,116)