Fair Value Measurements - Fair Values of Financial Assets and Liabilities, Including Derivative Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Earning assets
Tax indemnification receivable	$ 200,704	$ 240,311
Derivative instruments	27,493	1,193
Interest-bearing liabilities
Derivative instruments	29,602	24,643
Fair Value
Earning assets
Loans held for investment, net	12,837,892	10,228,399
Cash and cash equivalents	1,281,797	2,359,780
Available-for-sale investments	190,944	168,934
Accrued interest receivable	634,423	469,697
Tax indemnification receivable	200,704	240,311
Derivative instruments	38,746	5,238
Total earning assets	15,184,506	13,472,359
Interest-bearing liabilities
Short-term borrowings	710,005	0
Long-term borrowings	583,314	0
Accrued interest payable	23,309	16,082
Derivative instruments	40,855	28,688
Total interest-bearing liabilities	11,947,331	10,590,151
Fair Value | Money-market and savings accounts
Interest-bearing liabilities
Deposits	5,102,323	5,231,736
Fair Value | Certificates of deposit
Interest-bearing liabilities
Deposits	5,487,525	5,313,645
Carrying Value
Earning assets
Loans held for investment, net	11,909,148	9,509,786
Cash and cash equivalents	1,281,797	2,359,780
Available-for-sale investments	190,944	168,934
Accrued interest receivable	634,423	469,697
Tax indemnification receivable	200,704	240,311
Derivative instruments	38,746	5,238
Total earning assets	14,255,762	12,753,746
Interest-bearing liabilities
Short-term borrowings	710,005	0
Long-term borrowings	593,687	0
Accrued interest payable	23,309	16,082
Derivative instruments	40,855	28,688
Total interest-bearing liabilities	11,978,735	10,585,324
Carrying Value | Money-market and savings accounts
Interest-bearing liabilities
Deposits	5,102,323	5,231,736
Carrying Value | Certificates of deposit
Interest-bearing liabilities
Deposits	5,508,556	5,308,818
Difference
Earning assets
Loans held for investment, net	928,744	718,613
Cash and cash equivalents	0	0
Available-for-sale investments	0	0
Accrued interest receivable	0	0
Tax indemnification receivable	0	0
Derivative instruments	0	0
Total earning assets	928,744	718,613
Interest-bearing liabilities
Short-term borrowings	0	0
Long-term borrowings	10,373	0
Accrued interest payable	0	0
Derivative instruments	0	0
Total interest-bearing liabilities	31,404	(4,827)
Excess of net asset fair value over carrying value	960,148	713,786
Difference | Money-market and savings accounts
Interest-bearing liabilities
Deposits	0	0
Difference | Certificates of deposit
Interest-bearing liabilities
Deposits	$ 21,031	$ (4,827)