Fair Value Measurements - Fair Values of Financial Assets and Liabilities, Including Derivative Financial Instruments (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Earning assets
Loans held for investment, net, difference	$ 2,041,250	$ 2,105,495
Accrued interest receivable, difference	0
Tax indemnification receivable	153,470	168,011
Total earning assets, difference	2,041,250	2,105,495
Interest-bearing liabilities
Long-term borrowings, difference	18,969	(24,601)
Total interest-bearing liabilities, difference	55,127	(34,688)
Excess of net asset fair value over carrying value	2,096,377	2,070,807
Certificates of deposit
Interest-bearing liabilities
Deposits, difference	36,158	(10,087)
Fair Value
Earning assets
Loans held for investment, net	22,349,831	20,673,136
Cash and cash equivalents	2,043,789	1,534,339
Available-for-sale investments	178,145	244,088
Accrued interest receivable	1,161,161	967,482
Tax indemnification receivable	153,470	168,011
Derivative instruments	1,403	812
Total earning assets	25,887,799	23,587,868
Interest-bearing liabilities
Long-term borrowings	4,198,150	3,299,871
Accrued interest payable	46,658	35,363
Derivative instruments	92	2,584
Total interest-bearing liabilities	20,952,627	18,852,235
Fair Value | Money-market and savings accounts
Interest-bearing liabilities
Deposits	8,795,950	8,470,209
Fair Value | Certificates of deposit
Interest-bearing liabilities
Deposits	7,911,777	7,044,208
Carrying Value
Earning assets
Loans held for investment, net	20,308,581	18,567,641
Cash and cash equivalents	2,043,789	1,534,339
Available-for-sale investments	178,145	244,088
Accrued interest receivable	1,161,161	967,482
Tax indemnification receivable	153,470	168,011
Derivative instruments	1,403	812
Total earning assets	23,846,549	21,482,373
Interest-bearing liabilities
Long-term borrowings	4,217,119	3,275,270
Accrued interest payable	46,658	35,363
Derivative instruments	92	2,584
Total interest-bearing liabilities	21,007,754	18,817,547
Carrying Value | Money-market and savings accounts
Interest-bearing liabilities
Deposits	8,795,950	8,470,209
Deposits, difference	0
Carrying Value | Certificates of deposit
Interest-bearing liabilities
Deposits	$ 7,947,935	$ 7,034,121