Summary of Significant Accounting Policies - New Accounting Pronouncements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred income taxes	$ 59,178	$ 86,005
Income tax expense	$ (25,946)	(58,973)	$ (469)
Accounting Standards Update 2016-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred income taxes		1,000
Income tax expense		$ 900
Retained Earnings [Member] | Accounting Standards Update 2016-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment				$ 1,000