Shareholders' Equity - Additional Information (Detail) (USD $)	1 Months Ended	12 Months Ended			6 Months Ended
	Oct. 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014	Jun. 10, 2014
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Proceeds from the issuance of preferred stock, net	$ 110,300,000	$ 313,330,000	$ 0	$ 110,337,000
Preferred stock liquidation preference (in dollars per share)		$ 10,000	$ 10,000		$ 10,000
Premium for conversion price to concurrent common stock offering price		20.00%			20.00%
Common stock offering price, new issue (in dollars per share)	$ 5.00
Conversion ratio into common stock if closing sale price exceed prior period conversion price		130.00%			130.00%
Proceeds from Issuance of Convertible Preferred Stock		313,300,000
Premium, Conversion Price to Common Share Closing Price Prior to Series B Preferred Stock Offering						30.00%
Common Share Price, Last Reported Prior to Series B Preferred Stock Offering						$ 14.11
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Issuance of common stock (in shares)	9,200,000.0
Proceeds from issuance of common stock	43,500,000
Preferred Stock Conversions, Inducements		4,256,000	0	0
Accumulated other comprehensive losses attributable to pension and postretirement benefit obligations, net of tax		200,000	300,000	(1,000,000)	200,000
Treasury stock (in shares)		262,070	233,063		262,070
Series A Preferred Stock
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock dividend rate		6.00%
Conversion price (in dollars per share)		$ 6.00			$ 6.00
Convertible Preferred Stock, Shares Issued upon Conversion		1,666.67			1,666.67
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Issuance of common stock (in shares)	11,500
Conversion of Stock, Shares Converted		3,555
Preferred Stock Conversions, Inducements		$ 4,300,000
Series B Preferred Stock
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock dividend rate					6.00%
Conversion price (in dollars per share)		$ 18.34			$ 18.34
Convertible Preferred Stock, Shares Issued upon Conversion		545.17			545.17
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Issuance of common stock (in shares)		32,500
Common Stock
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Stock Issued During Period, Shares, Conversion of Convertible Securities		5,900,000