Loans Receivable and Allowance for Credit Losses (Loan Purchases, Sales and Transfers) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Loans Receivable and Allowance for Credit Losses
Loans transferred from held-for-investment to held-for-sale	$ 33,060,000	$ 81,166,000	$ 143,283,000	$ 173,394,000
Sales	46,768,000	78,776,000	161,633,000	173,519,000
Purchases	12,510,000	178,471,000	145,690,000	326,285,000
Write-down of loans transferred from loans held-for-investment to loans held-for-sale recorded to allowance for loan losses	0	317,000	0	390,000
Net gains from sales of loans held-for-sale during the period	132,000	15,000	1,100,000	930,000
Commercial and industrial (“C&I”) | Originated
Loans Receivable and Allowance for Credit Losses
Sales		55,700,000		132,200,000
Commercial and industrial (“C&I”) | Single-family residential | Originated
Loans Receivable and Allowance for Credit Losses
Sales	46,800,000		161,600,000
Loans sold in secondary market | Purchased
Loans Receivable and Allowance for Credit Losses
Sales	0	23,100,000	0	41,300,000
Commercial lending | Commercial and industrial (“C&I”)
Loans Receivable and Allowance for Credit Losses
Loans transferred from held-for-investment to held-for-sale	33,060,000	79,593,000	136,033,000	155,166,000
Sales	33,060,000	76,031,000	136,033,000	151,677,000
Purchases	12,503,000	159,100,000	143,086,000	266,294,000
Write-down of loans transferred from loans held-for-investment to loans held-for-sale recorded to allowance for loan losses	20,378,000	11,745,000	32,355,000	28,989,000
Commercial lending | Commercial real estate (“CRE”)
Loans Receivable and Allowance for Credit Losses
Loans transferred from held-for-investment to held-for-sale	0	0	7,250,000	16,655,000
Sales	0	0	7,250,000	16,655,000
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	320,000	0	1,274,000	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	0
Sales	0	0	0	0
Purchases	7,000	1,734,000	1,520,000	5,952,000
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	1,573,000	0	1,573,000
Sales	0	1,573,000	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	13,708,000	1,172,000	18,350,000	3,614,000
Purchases	0	17,637,000	1,084,000	54,039,000
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