Long-Term Debt - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended				3 Months Ended	6 Months Ended	1 Months Ended	6 Months Ended		12 Months Ended	1 Months Ended	6 Months Ended		12 Months Ended
	Jun. 30, 2013	Mar. 31, 2013	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Long-term Debt Maximum	Dec. 31, 2012 Long-term Debt Maximum	Jun. 30, 2013 Commercial Loan Warehouse Facility	Jun. 30, 2013 Commercial Loan Warehouse Facility	Dec. 31, 2010 Trust Preferred Securities	Jun. 30, 2013 Trust Preferred Securities	Jun. 30, 2012 Trust Preferred Securities	Dec. 31, 2006 Trust Preferred Securities	Jul. 31, 2009 Subordinated Notes	Jun. 30, 2013 Subordinated Notes	Jun. 30, 2012 Subordinated Notes	Dec. 31, 2007 Subordinated Notes
Debt Instrument [Line Items]
Line of credit facility outstanding amount							$ 17,000,000	$ 17,000,000
Line of credit facility, maximum borrowing capacity							150,000,000	150,000,000
Line of credit facility, maturity period								27 months
Line of credit facility, average balance							17,000,000	11,000,000
Interest expense yield on borrowing							5.50%	5.59%
Fair value of commercial loans pledged as collateral	1,200,000,000		1,200,000,000				26,000,000	26,000,000
Convertible notes		287,500,000
Debt Instrument interest rate		4.625%
Debt instrument maturity year		2018
Debt instrument redemption date		Apr. 15, 2018
Net proceeds from issuance of convertible debt		279,000,000
Interest expense yield	5.53%		5.48%							2.65%	2.91%			2.65%	2.91%
Accrued interest payable	4,000,000		4,000,000
Convertible senior notes conversion rate			41.1320
Debt instrument convertible base principal amount of conversion	1,000		1,000
Convertible senior notes conversion per share	$ 24.31		$ 24.31
Debt instrument face amount												100,000,000				50,000,000
Debt instrument quarterly floating coupon rate basis												Three-month LIBOR plus 2.25%				Six-month LIBOR plus 2.25%
Debt instrument quarterly floating coupon rate												2.25%				2.25%
Debt instrument due date			Apr. 15, 2018									Jan. 30, 2037				Jul. 30, 2037
Percentage of yield of debt securities										6.89%	6.88%			6.89%	6.88%
Earliest optional redemption date without penalty										Jan. 30, 2012				Jul. 30, 2012
Principal amount of debt repurchased									500,000				10,000,000
Accrued interest payable balance on long-term debt	$ 8,682,000		$ 8,682,000	$ 4,592,000	$ 1,000,000	$ 1,000,000