Summary of Significant Accounting Policies Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Basis for Allocating Income to Different Common Stock Classes									The basic and diluted earnings per share of Class B common stock are one half the earnings per share of the Class A common stock.
Net income (loss)	$ (1,432)	$ (7,109)	$ (2,558)	$ 37	$ (44,204)	$ 3,449	$ 572	$ 2,056	$ (11,062)	$ (38,127)	$ 1,969
Net Income Allocated to Class A Common Stock									(10,950)	(37,742)	1,949
Net Income Allocated to Class B Common Stock									$ (112)	$ (385)	$ 20
Weighted Average Number of Shares Outstanding, Basic									50,082	50,082	50,082
Weighted Average Number of Shares Outstanding, Diluted									50,141	50,082	50,082
Common Class A [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Weighted Average Number of Shares Outstanding, Basic									49,080	49,080	49,080
Weighted Average Number of Shares Outstanding, Diluted									49,139	49,080	49,080
Basic and diluted earnings (losses) per share (in dollars per share)	$ (0.03)	$ (0.14)	$ (0.05)	$ 0.00	$ (0.89)	$ 0.07	$ 0.01	$ 0.04	$ (0.22)	$ (0.77)	$ 0.04
Common Class B [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Weighted Average Number of Shares Outstanding, Basic and Diluted									1,002	1,002	1,002
Basic and diluted earnings (losses) per share (in dollars per share)	$ (0.01)	$ (0.07)	$ (0.03)	$ 0.00	$ (0.44)	$ 0.03	$ 0.01	$ 0.02	$ (0.11)	$ (0.38)	$ 0.02