Earnings Per Share - Summary of Numerator and Denominator of Basic and Fully Diluted Earnings Per Common Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income	$ 17,620	$ 20,387
Less: Preferred stock dividends	3	(34)
Less: Income attributable to participating securities	(1,180)	(459)
Basic Earnings Per Share:
Income allocated to common stockholders, Income (Numerator)	16,443	19,894
Income allocated to common stockholders, Shares (Denominator)	10,261	10,650
Income allocated to common stockholders, Per Share Amount	$ 1.60	$ 1.87
Diluted Earnings Per Share:
Income available to common stockholders and assumed conversions, Income (Numerator)	17,511	19,928
Income available to common stockholders and assumed conversions, Shares (Denominator)	12,138	11,031
Income available to common stockholders and assumed conversions, Per Share Amount	$ 1.44	$ 1.81
Warrants [Member]
Effect of Dilutive Securities:
Dilutive Securities, Shares (Denominator)	1,649
Convertible senior notes (Numerator)	0
Convertible Preferred Stock [Member]
Effect of Dilutive Securities:
Dilutive Securities, Income (Numerator)
Dilutive Securities, Shares (Denominator)	1,071
Stock Options [Member]
Effect of Dilutive Securities:
Dilutive Securities, Shares (Denominator)	(3)	34