Investment Securities - Summary of Unrealized Loss Positions of Available for Sale TRUP CDOs and Single Issue Trust Preferred Securities (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Assumptions Utilized In Other Than Temporary Impairment Analysis Of Securities [Line Items]
Amortized Cost	$ 1,180,016,000	$ 813,049,000
Fair Value	1,180,386,000	775,284,000
Trup CDOs and Single Issue Trust Preferred Securities [Member]
Assumptions Utilized In Other Than Temporary Impairment Analysis Of Securities [Line Items]
Amortized Cost	51,328,000
Fair Value	39,558,000
Unrealized Loss	11,770,000
Senior - Bank [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Assumptions Utilized In Other Than Temporary Impairment Analysis Of Securities [Line Items]
Amortized Cost	7,725,000
Fair Value	6,660,000
Unrealized Loss	1,065,000
Mezzanine - Bank (now in senior position) [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Assumptions Utilized In Other Than Temporary Impairment Analysis Of Securities [Line Items]
Amortized Cost	12,218,000
Fair Value	9,833,000
Unrealized Loss	2,385,000
Mezzanine - Bank [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Assumptions Utilized In Other Than Temporary Impairment Analysis Of Securities [Line Items]
Amortized Cost	26,216,000
Fair Value	18,929,000
Unrealized Loss	7,287,000
Mezzanine - Bank & Insurance (combination) [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Assumptions Utilized In Other Than Temporary Impairment Analysis Of Securities [Line Items]
Amortized Cost	5,169,000
Fair Value	4,136,000
Unrealized Loss	1,033,000
Investment Grade [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Assumptions Utilized In Other Than Temporary Impairment Analysis Of Securities [Line Items]
Amortized Cost	5,000,000
Investment Grade [Member] | Senior - Bank [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Assumptions Utilized In Other Than Temporary Impairment Analysis Of Securities [Line Items]
Amortized Cost	5,000,000
Investment Grade [Member] | Mezzanine - Bank (now in senior position) [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Assumptions Utilized In Other Than Temporary Impairment Analysis Of Securities [Line Items]
Amortized Cost	0
Investment Grade [Member] | Mezzanine - Bank [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Assumptions Utilized In Other Than Temporary Impairment Analysis Of Securities [Line Items]
Amortized Cost	0
Investment Grade [Member] | Mezzanine - Bank & Insurance (combination) [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Assumptions Utilized In Other Than Temporary Impairment Analysis Of Securities [Line Items]
Amortized Cost	0
Split Rated [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Assumptions Utilized In Other Than Temporary Impairment Analysis Of Securities [Line Items]
Amortized Cost	0
Split Rated [Member] | Senior - Bank [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Assumptions Utilized In Other Than Temporary Impairment Analysis Of Securities [Line Items]
Amortized Cost	0
Split Rated [Member] | Mezzanine - Bank (now in senior position) [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Assumptions Utilized In Other Than Temporary Impairment Analysis Of Securities [Line Items]
Amortized Cost	0
Split Rated [Member] | Mezzanine - Bank [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Assumptions Utilized In Other Than Temporary Impairment Analysis Of Securities [Line Items]
Amortized Cost	0
Split Rated [Member] | Mezzanine - Bank & Insurance (combination) [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Assumptions Utilized In Other Than Temporary Impairment Analysis Of Securities [Line Items]
Amortized Cost	0
Below Investment Grade [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Assumptions Utilized In Other Than Temporary Impairment Analysis Of Securities [Line Items]
Amortized Cost	46,328,000
Below Investment Grade [Member] | Senior - Bank [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Assumptions Utilized In Other Than Temporary Impairment Analysis Of Securities [Line Items]
Amortized Cost	2,725,000
Below Investment Grade [Member] | Mezzanine - Bank (now in senior position) [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Assumptions Utilized In Other Than Temporary Impairment Analysis Of Securities [Line Items]
Amortized Cost	12,218,000
Below Investment Grade [Member] | Mezzanine - Bank [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Assumptions Utilized In Other Than Temporary Impairment Analysis Of Securities [Line Items]
Amortized Cost	26,216,000
Below Investment Grade [Member] | Mezzanine - Bank & Insurance (combination) [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Assumptions Utilized In Other Than Temporary Impairment Analysis Of Securities [Line Items]
Amortized Cost	$ 5,169,000