Related Party Transactions (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) ft² Director shares	Dec. 31, 2016 USD ($) shares
Related Party Transaction [Line Items]
Number of board of directors | Director	2
Rental expense for operating leases	$ 1,306	$ 1,277
Payment of dividends on Series D Preferred Stock	399	399
Series D Preferred Stock [Member]
Related Party Transaction [Line Items]
Payment of dividends on Series D Preferred Stock	$ 399	399
Affiliated Entity [Member]
Related Party Transaction [Line Items]
Office and covered garage space leased | ft²	49,586
Rental expense for operating leases	$ 866	882
Services purchased from related party	54	215
Members of Management [Member]
Related Party Transaction [Line Items]
Aggregate carrying value of investments in Gray	14,407	10,305
Premiums paid by Gray for group accident plan	$ 597	$ 478
Members of Management [Member] | Class A common stock [Member]
Related Party Transaction [Line Items]
Shares of Gray common stock owned (in shares) | shares	880,272	880,272
Members of Management [Member] | Common Stock [Member]
Related Party Transaction [Line Items]
Shares of Gray common stock owned (in shares) | shares	106,000	106,000