Loans Receivable and Allowance for Credit Losses (Loan Purchases, Sales and Transfers) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Loans Receivable and Allowance for Credit Losses
Loans transferred from held-for-investment to held-for-sale	$ 77,960,000	$ 74,512,000	$ 363,591,000	$ 418,489,000
Loans transferred from held-for-sale to held-for-investment	2,306,000		2,306,000	0
Sales	93,418,000	91,247,000	386,621,000	455,952,000
Purchases	61,086,000	72,416,000	450,908,000	441,112,000
Write-down of loans transferred from loans held-for-investment to loans held-for-sale recorded to allowance for loan losses	110,000	232,000	13,500,000	441,000
Net gains from sales of loans held-for-sale during the period, excluding lower of cost or fair value adjustment	1,100,000	2,400,000	5,100,000	6,700,000
Lower of cost or fair value adjustment	0	0	0	(61,000)
Commercial and industrial and single-family residential | Originated
Loans Receivable and Allowance for Credit Losses
Sales	58,900,000
Commercial and industrial | Originated
Loans Receivable and Allowance for Credit Losses
Sales			252,100,000
Commercial and industrial and commercial real estate | Originated
Loans Receivable and Allowance for Credit Losses
Sales		33,800,000		101,400,000
Loans sold in secondary market | Purchased
Loans Receivable and Allowance for Credit Losses
Sales	34,500,000	57,400,000	134,500,000	354,500,000
Commercial lending | Commercial and industrial (“C&I”)
Loans Receivable and Allowance for Credit Losses
Loans transferred from held-for-investment to held-for-sale	53,149,000	58,786,000	298,989,000	382,862,000
Loans transferred from held-for-sale to held-for-investment	2,306,000		2,306,000
Sales	62,744,000	69,750,000	305,435,000	382,870,000
Purchases	47,809,000	63,590,000	398,171,000	431,318,000
Commercial lending | Commercial real estate (“CRE”)
Loans Receivable and Allowance for Credit Losses
Loans transferred from held-for-investment to held-for-sale	9,830,000	14,803,000	49,621,000	33,236,000
Loans transferred from held-for-sale to held-for-investment	0		0
Sales	9,830,000	14,803,000	49,621,000	33,236,000
Purchases	0	0	0	0
Commercial lending | Real estate loan | Multifamily residential
Loans Receivable and Allowance for Credit Losses
Loans transferred from held-for-investment to held-for-sale	0	0	0	532,000
Loans transferred from held-for-sale to held-for-investment	0		0
Sales	0	0	0	532,000
Purchases	2,518,000	178,000	5,953,000	1,018,000
Commercial lending | Construction and land
Loans Receivable and Allowance for Credit Losses
Loans transferred from held-for-investment to held-for-sale	0	923,000	0	1,610,000
Loans transferred from held-for-sale to held-for-investment	0		0
Sales	0	923,000	0	1,610,000
Purchases	0	0	0	0
Consumer lending | Real estate loan | Single-family residential
Loans Receivable and Allowance for Credit Losses
Loans transferred from held-for-investment to held-for-sale	14,981,000	0	14,981,000	249,000
Loans transferred from held-for-sale to held-for-investment	0		0
Sales	20,844,000	5,771,000	31,565,000	15,513,000
Purchases	10,759,000	8,648,000	46,784,000	8,776,000
Consumer lending | Other consumer
Loans Receivable and Allowance for Credit Losses
Loans transferred from held-for-investment to held-for-sale	0	0	0	0
Loans transferred from held-for-sale to held-for-investment	0		0
Sales	0	0	0	22,191,000
Purchases	$ 0	$ 0	$ 0	$ 0