Stockholders' Equity (Detail) $ / shares in Units, $ in Millions		1 Months Ended		12 Months Ended
	Sep. 16, 2011 $ / shares shares	Jun. 30, 2014 USD ($) shares	Jun. 30, 2009 $ / shares shares	Dec. 31, 2017 vote class shares	Dec. 31, 2016 shares
Class of Stock [Line Items]
Total stock dividend authorized to issue (in shares)				268,830,609
Number of classes of stock | class				4
Preferred stock, shares authorized				100,000,000
Preferred stock, shares outstanding (in shares)				0	0
Preferred stock, par/stated value (USD per share) | $ / shares	$ 0.01
Shares in treasury stock | $		$ 25.0
2009 warrants
Class of Stock [Line Items]
Warrants issued (in shares)			156,250
Exercisable price of warrants to purchase common stock (price per share) | $ / shares			$ 1.17
Warrants converted (in shares)				0	0
Number of warrants outstanding				40,057	40,057
Company Warrants
Class of Stock [Line Items]
Number of warrants outstanding				31,955
Warrants exercised (in shares)				0
Equity Investment
Class of Stock [Line Items]
Number of warrants outstanding	1,000,000			1,000,000
Crestview Warrants
Class of Stock [Line Items]
Exercisable price of warrants to purchase common stock (price per share) | $ / shares	$ 34.56
Citadel Acquisition
Class of Stock [Line Items]
Warrants issued (in shares)		300,000
Warrants held in reserve for issuance (in shares)	300,000
Class A Common Stock
Class of Stock [Line Items]
Common stock, shares authorized				93,750,000	93,750,000
Number of votes for each share | vote				1
Common stock, shares issued				32,031,954	32,031,954
Common stock, shares outstanding				29,225,765	29,225,765
Warrants exercised (in shares)				43,192
Class A Common Stock | Citadel Acquisition
Class of Stock [Line Items]
Common stock, shares issued	9,000,000
Class A Common Stock | Minimum
Class of Stock [Line Items]
Class A common stock following conversion				4.99%
Class B Common Stock
Class of Stock [Line Items]
Common stock, shares authorized				75,000,000
Common stock, shares issued				0	0
Common stock, shares outstanding				0	0
Class C Common Stock
Class of Stock [Line Items]
Common stock, shares authorized				80,609	80,609
Number of votes for each share | vote				10
Common stock, shares issued				80,609	80,609
Common stock, shares outstanding				80,609	80,609