Loans Receivable and Allowance for Credit Losses (Loan Purchases, Sales and Transfers) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Loans Receivable and Allowance for Credit Losses
Loans transferred from held-for-investment to held-for-sale	$ 89,394,000	$ 49,040,000	$ 253,302,000	$ 222,434,000
Sales	124,084,000	55,663,000	306,342,000	229,182,000
Purchases	18,132,000	68,965,000	163,822,000	395,250,000
Write-down of loans transferred from loans held-for-investment to loans held-for-sale recorded to allowance for loan losses	2,800,000	36,000	2,800,000	426,000
Net gains on sales of loans	361,000	2,037,000	1,443,000	2,967,000
Commercial and industrial (“C&I”) | Originated
Loans Receivable and Allowance for Credit Losses
Sales		47,800,000		180,000,000.0
Commercial and industrial (“C&I”) | Single-family residential | Originated
Loans Receivable and Allowance for Credit Losses
Sales	112,300,000		294,600,000
Loans sold in secondary market | Purchased
Loans Receivable and Allowance for Credit Losses
Sales	11,800,000	7,900,000	11,800,000	49,200,000
Commercial lending | Commercial and industrial (“C&I”)
Loans Receivable and Allowance for Credit Losses
Loans transferred from held-for-investment to held-for-sale	89,394,000	34,071,000	246,052,000	189,237,000
Sales	92,237,000	37,986,000	248,895,000	189,663,000
Purchases	0	38,047,000	143,086,000	304,341,000
Write-down of loans transferred from loans held-for-investment to loans held-for-sale recorded to allowance for loan losses	25,111,000	25,098,000	57,466,000	54,087,000
Commercial lending | Commercial real estate (“CRE”)
Loans Receivable and Allowance for Credit Losses
Loans transferred from held-for-investment to held-for-sale	0	14,969,000	7,250,000	31,624,000
Sales	0	14,969,000	7,250,000	31,624,000
Purchases	0	0	0	0
Write-down of loans transferred from loans held-for-investment to loans held-for-sale recorded to allowance for loan losses	1,414,000	1,021,000	2,688,000	1,021,000
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	0
Sales	0	0	0	0
Purchases	838,000	1,350,000	2,358,000	7,302,000
Write-down of loans transferred from loans held-for-investment to loans held-for-sale recorded to allowance for loan losses	0	0	0	0
Commercial lending | Construction and land
Loans Receivable and Allowance for Credit Losses
Loans transferred from held-for-investment to held-for-sale	0	0	0	1,573,000
Sales	0	0	0	1,573,000
Purchases	0	0	0	0
Write-down of loans transferred from loans held-for-investment to loans held-for-sale recorded to allowance for loan losses	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	0	0	0	0
Sales	31,847,000	2,708,000	50,197,000	6,322,000
Purchases	17,294,000	29,568,000	18,378,000	83,607,000
Write-down of loans transferred from loans held-for-investment to loans held-for-sale recorded to allowance for loan losses	$ 0	$ 11,000	$ 0	$ 11,000