Fair Value Measurements - Fair Values of Financial Assets and Liabilities, Including Derivative Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Earning assets
Loans held for investment, net, difference	$ 1,973,053	$ 1,382,864
Cash and cash equivalents, difference	0	0
Tax indemnification receivable	214,496	259,532
Derivative instruments	0	0
Total earning assets, difference	1,973,053	1,382,864
Interest-bearing liabilities
Long-term borrowings, difference	(25,765)	7,874
Total interest-bearing liabilities, difference	(42,674)	(31,565)
Excess of net asset fair value over carrying value	1,930,379	1,351,299
Certificates of deposit
Interest-bearing liabilities
Certificates of deposit, difference	(16,909)	(39,439)
Fair Value
Earning assets
Loans held for investment, net	20,013,518	16,520,786
Cash and cash equivalents	1,247,764	1,918,793
Available-for-sale investments	232,549	208,603
Accrued interest receivable	1,019,735	766,106
Tax indemnification receivable	214,496	259,532
Derivative instruments	636	7,808
Total earning assets	22,728,698	19,681,628
Interest-bearing liabilities
Short-term borrowings	300,000	0
Long-term borrowings	2,764,427	2,160,105
Accrued interest payable	36,299	21,058
Derivative instruments	8,636	25,937
Total interest-bearing liabilities	18,159,795	15,681,529
Fair Value | Money-market and savings accounts
Interest-bearing liabilities
Deposits	8,480,477	7,963,925
Fair Value | Certificates of deposit
Interest-bearing liabilities
Deposits	6,569,956	5,510,504
Carrying Value
Earning assets
Loans held for investment, net	18,040,465	15,137,922
Cash and cash equivalents	1,247,764	1,918,793
Available-for-sale investments	232,549	208,603
Accrued interest receivable	1,019,735	766,106
Tax indemnification receivable	214,496	259,532
Derivative instruments	636	7,808
Total earning assets	20,755,645	18,298,764
Interest-bearing liabilities
Short-term borrowings	300,000	0
Long-term borrowings	2,738,662	2,167,979
Accrued interest payable	36,299	21,058
Derivative instruments	8,636	25,937
Total interest-bearing liabilities	18,117,121	15,649,964
Carrying Value | Money-market and savings accounts
Interest-bearing liabilities
Deposits	8,480,477	7,963,925
Carrying Value | Certificates of deposit
Interest-bearing liabilities
Deposits	$ 6,553,047	$ 5,471,065