Segment Information - Financial Information by Segment (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Segment Reporting Information [Line Items]
Interest income		$ 63,373	$ 57,993	$ 127,119	$ 113,469
Interest expense		(23,008)	(21,151)	(46,969)	(40,211)
Net Interest Income		40,365	36,842	80,150	73,258
Provision for loan losses		261	315	55	(967)
Mortgage banking and investment activities	[1]	5,659	2,189	6,437	(4,181)
MSR income (loss), net		830	(1,777)	(10,094)	(1,171)
Other income		1,299	0	2,108	0
Realized gains, net		6,316	1,063	10,622	2,155
Total non-interest income (loss)		14,104	1,475	9,073	(3,197)
Direct operating expenses		(25,218)	(22,282)	(50,281)	(42,254)
(Provision for) benefit from income taxes		(2,448)	(333)	2,868	1,510
Net Income		27,064	16,017	41,865	28,350
Non-cash amortization income (expense)		8,207	8,262	16,968	17,338
Hedging allocations		0		0
Operating Segments | Residential Mortgage Banking
Segment Reporting Information [Line Items]
Interest income		9,976	12,438	25,771	23,104
Interest expense		(3,298)	(2,161)	(7,076)	(3,482)
Net Interest Income		6,678	10,277	18,695	19,622
Provision for loan losses		0	0	0	0
Mortgage banking and investment activities		4,833	1,342	7,052	276
MSR income (loss), net		0	0	0	0
Other income		0	0
Realized gains, net		0	0	0	0
Total non-interest income (loss)		4,833	1,342	7,052	276
Direct operating expenses		(11,033)	(9,501)	(21,936)	(16,595)
(Provision for) benefit from income taxes		865	259	872	94
Net Income		1,343	2,377	4,683	3,397
Non-cash amortization income (expense)		(44)	(36)	(90)	(88)
Hedging allocations		2,803		2,803
Operating Segments | Residential Investments
Segment Reporting Information [Line Items]
Interest income		34,249	27,924	64,261	55,519
Interest expense		(2,660)	(3,116)	(5,469)	(5,966)
Net Interest Income		31,589	24,808	58,792	49,553
Provision for loan losses		0	0	0	0
Mortgage banking and investment activities		(1,104)	(3,788)	(1,123)	(9,746)
MSR income (loss), net		830	(1,777)	(10,094)	(1,171)
Other income		1,299	0	2,108
Realized gains, net		6,316	992	10,622	1,979
Total non-interest income (loss)		7,341	(4,573)	1,513	(8,938)
Direct operating expenses		(1,171)	(770)	(2,289)	(1,865)
(Provision for) benefit from income taxes		(3,768)	149	(258)	1,676
Net Income		33,991	19,614	57,758	40,426
Non-cash amortization income (expense)		9,324	10,586	19,162	21,833
Hedging allocations		(2,753)		(2,753)
Operating Segments | Commercial Mortgage Banking and Investments
Segment Reporting Information [Line Items]
Interest income		12,679	11,217	23,593	21,601
Interest expense		(3,497)	(4,404)	(6,986)	(7,708)
Net Interest Income		9,182	6,813	16,607	13,893
Provision for loan losses		261	(289)	55	(944)
Mortgage banking and investment activities		2,614	4,981	2,321	5,814
MSR income (loss), net		0	0	0	0
Other income		0	0
Realized gains, net		0	0	0	0
Total non-interest income (loss)		2,614	4,981	2,321	5,814
Direct operating expenses		(3,020)	(2,180)	(6,502)	(4,806)
(Provision for) benefit from income taxes		(143)	(750)	710	(395)
Net Income		8,894	8,575	13,191	13,562
Non-cash amortization income (expense)		(78)	(215)	(128)	(388)
Hedging allocations		0		0
Corporate/Other
Segment Reporting Information [Line Items]
Interest income		6,469	6,414	13,494	13,245
Interest expense		(13,553)	(11,470)	(27,438)	(23,055)
Net Interest Income		(7,084)	(5,056)	(13,944)	(9,810)
Provision for loan losses		0	604	0	(23)
Mortgage banking and investment activities		(684)	(346)	(1,813)	(525)
MSR income (loss), net		0	0	0	0
Other income		0	0
Realized gains, net		0	71	0	176
Total non-interest income (loss)		(684)	(275)	(1,813)	(349)
Direct operating expenses		(9,994)	(9,831)	(19,554)	(18,988)
(Provision for) benefit from income taxes		598	9	1,544	135
Net Income		(17,164)	(14,549)	(33,767)	(29,035)
Non-cash amortization income (expense)		(995)	$ (2,073)	(1,976)	$ (4,019)
Hedging allocations		$ (50)		$ (50)

[1] For the three months ended June 30, 2015, there were no other-than-temporary impairments. For the three months ended June 30, 2014, other-than-temporary impairments were $2,915, of which $264 were recognized through the Income Statement and $2,651 were recognized in Accumulated Other Comprehensive Income.For the six months ended June 30, 2015, there were no other-then-temporary impairments. For the six months ended June 30, 2014, other-than-temporary impairments were $4,585, of which $377 were recognized through the Income Statement, and $4,208 were recognized in Accumulated Other Comprehensive Income.