Earnings Per Share - Summary of Numerator and Denominator of Basic and Diluted Earnings Per Common Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income	$ 14,052	$ 13,378	$ 48,102	$ 50,000
Less: Preferred stock dividends		(22)	4	(88)
Less: Income attributable to participating securities	(1,024)	(823)	(3,415)	(2,205)
Basic Earnings Per Share:
Income allocated to common stockholders, Income (Numerator)	13,028	12,533	44,691	47,707
Income allocated to common stockholders, Shares (Denominator)	9,736	10,749	9,972	10,696
Income allocated to common stockholders, Per Share Amount	$ 1.34	$ 1.17	$ 4.48	$ 4.46
Diluted Earnings Per Share:
Income available to common stockholders and assumed conversions, Income (Numerator)	14,118	12,555	47,929	47,795
Income available to common stockholders and assumed conversions, Shares (Denominator)	11,518	11,078	11,787	11,053
Income available to common stockholders and assumed conversions, Per Share Amount	$ 1.23	$ 1.13	$ 4.07	$ 4.32
Convertible Senior Notes [Member]
Effect of Dilutive Securities:
Dilutive Securities, Income (Numerator)	1,090		3,242
Dilutive Securities, Shares (Denominator)	1,649		1,649
Convertible Preferred Stock [Member]
Effect of Dilutive Securities:
Dilutive Securities, Income (Numerator)		$ 22	$ (4)	$ 88
Dilutive Securities, Shares (Denominator)		165	27	195
Stock Options [Member]
Effect of Dilutive Securities:
Dilutive Securities, Shares (Denominator)	133	164	139	162