Fair Value Measurements - Fair Values of Financial Assets and Liabilities, Including Derivative Financial Instruments (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Earning assets
Loans held for investment, net, difference	$ 2,097,587	$ 2,105,495
Cash and cash equivalents, difference	0	0
Tax indemnification receivable	169,242	168,011
Derivative instruments	0	0
Total earning assets, difference	2,097,587	2,105,495
Interest-bearing liabilities
Long-term borrowings, difference	12,649	(24,601)
Total interest-bearing liabilities, difference	(375,315)	(34,688)
Excess of net asset fair value over carrying value	1,722,272	2,070,807
Certificates of deposit
Interest-bearing liabilities
Certificates of deposit, difference	(387,964)	(10,087)
Fair Value
Earning assets
Loans held for investment, net	22,264,191	20,673,136
Cash and cash equivalents	1,435,649	1,534,339
Available-for-sale investments	229,114	244,088
Accrued interest receivable	1,063,449	967,482
Tax indemnification receivable	169,242	168,011
Derivative instruments	794	812
Total earning assets	25,162,439	23,587,868
Interest-bearing liabilities
Long-term borrowings	3,731,696	3,299,871
Accrued interest payable	46,396	35,363
Derivative instruments	1,089	2,584
Total interest-bearing liabilities	20,664,151	18,852,235
Fair Value | Money-market and savings accounts
Interest-bearing liabilities
Deposits	8,789,020	8,470,209
Fair Value | Certificates of deposit
Interest-bearing liabilities
Deposits	8,095,950	7,044,208
Carrying Value
Earning assets
Loans held for investment, net	20,166,604	18,567,641
Cash and cash equivalents	1,435,649	1,534,339
Available-for-sale investments	229,114	244,088
Accrued interest receivable	1,063,449	967,482
Tax indemnification receivable	169,242	168,011
Derivative instruments	794	812
Total earning assets	23,064,852	21,482,373
Interest-bearing liabilities
Long-term borrowings	3,744,345	3,275,270
Accrued interest payable	46,396	35,363
Derivative instruments	1,089	2,584
Total interest-bearing liabilities	20,288,836	18,817,547
Carrying Value | Money-market and savings accounts
Interest-bearing liabilities
Deposits	8,789,020	8,470,209
Carrying Value | Certificates of deposit
Interest-bearing liabilities
Deposits	$ 7,707,986	$ 7,034,121