Financing Arrangements - Additional Information (Detail) (USD $)	Jan. 05, 2015	Jan. 30, 2014	Mar. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Loans outstanding	$ 0
7.50% Subordinated Notes [Member]
Debt Instrument [Line Items]
Principal available		$ 150,000,000
Debt instrument, interest rate, stated percentage		7.50%
Series B Preferred Stock [Member]
Debt Instrument [Line Items]
Preferred stock, shares issued	600,000		600,000	0
Affiliates of KKR [Member] | Series B Preferred Stock [Member]
Debt Instrument [Line Items]
Preferred stock, shares issued	200,000