Significant Accounting Policies and Basis of Presentation - Impact of ASC 326 (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019	Mar. 31, 2020	Jan. 01, 2020	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201613Member
Loans and leases receivable, net of allowance for loan losses, Estimated Fair Value		$ 2,245,758
Loans and leases receivable	$ 7,272,447	7,318,988
Allowance for credit losses on loans and leases	(159,905)	(56,379)	$ (149,283)	$ (136,200)	$ (48,388)	$ (43,679)	$ (39,972)
Total loans and leases receivable, net of allowance for credit losses on loans and leases	14,666,133	9,508,367
Allowance for credit losses on lending-related commitments		49
Net deferred tax (asset) liability		11,740
Retained earnings	$ 338,665	381,519
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and leases receivable, net of allowance for loan losses, Estimated Fair Value				0
Loans and leases receivable				232
Allowance for credit losses on loans and leases		(79,829)		(79,829)
Total loans and leases receivable, net of allowance for credit losses on loans and leases				(79,596)
Allowance for credit losses on lending-related commitments				3,388
Net deferred tax (asset) liability				(21,510)
Retained earnings				(61,475)
Cumulative Effect, Period Of Adoption, Adjusted Balance
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and leases receivable, net of allowance for loan losses, Estimated Fair Value				2,245,758
Loans and leases receivable				7,319,220
Allowance for credit losses on loans and leases				(136,208)
Total loans and leases receivable, net of allowance for credit losses on loans and leases				9,428,771
Allowance for credit losses on lending-related commitments				3,437
Net deferred tax (asset) liability				(9,770)
Retained earnings				320,044
Commercial Portfolio Segment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and leases receivable		5,690,820
Commercial Portfolio Segment | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and leases receivable				151
Commercial Portfolio Segment | Cumulative Effect, Period Of Adoption, Adjusted Balance
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and leases receivable				5,690,971
Commercial Portfolio Segment | Multi-family
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and leases receivable		1,907,331
Commercial Portfolio Segment | Multi-family | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and leases receivable				7
Commercial Portfolio Segment | Multi-family | Cumulative Effect, Period Of Adoption, Adjusted Balance
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and leases receivable				1,907,338
Commercial Portfolio Segment | Commercial and industrial
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and leases receivable		1,891,152
Commercial Portfolio Segment | Commercial and industrial | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and leases receivable				3
Commercial Portfolio Segment | Commercial and industrial | Cumulative Effect, Period Of Adoption, Adjusted Balance
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and leases receivable				1,891,155
Commercial Portfolio Segment | Commercial real estate owner occupied
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and leases receivable		551,948
Commercial Portfolio Segment | Commercial real estate owner occupied | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and leases receivable				100
Commercial Portfolio Segment | Commercial real estate owner occupied | Cumulative Effect, Period Of Adoption, Adjusted Balance
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and leases receivable				552,048
Commercial Portfolio Segment | Commercial real estate non-owner occupied
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and leases receivable		1,222,772
Commercial Portfolio Segment | Commercial real estate non-owner occupied | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and leases receivable				41
Commercial Portfolio Segment | Commercial real estate non-owner occupied | Cumulative Effect, Period Of Adoption, Adjusted Balance
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and leases receivable				1,222,813
Commercial Portfolio Segment | Construction
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and leases receivable		117,617
Commercial Portfolio Segment | Construction | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and leases receivable				0
Commercial Portfolio Segment | Construction | Cumulative Effect, Period Of Adoption, Adjusted Balance
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and leases receivable				117,617
Consumer Portfolio Segment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and leases receivable		1,628,168
Consumer Portfolio Segment | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and leases receivable				81
Consumer Portfolio Segment | Cumulative Effect, Period Of Adoption, Adjusted Balance
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and leases receivable				1,628,249
Consumer Portfolio Segment | Residential real estate
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and leases receivable		382,634
Consumer Portfolio Segment | Residential real estate | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and leases receivable				32
Consumer Portfolio Segment | Residential real estate | Cumulative Effect, Period Of Adoption, Adjusted Balance
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and leases receivable				382,666
Consumer Portfolio Segment | Manufactured housing
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and leases receivable		71,359
Consumer Portfolio Segment | Manufactured housing | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and leases receivable				37
Consumer Portfolio Segment | Manufactured housing | Cumulative Effect, Period Of Adoption, Adjusted Balance
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and leases receivable				71,396
Consumer Portfolio Segment | Other consumer
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and leases receivable		$ 1,174,175
Consumer Portfolio Segment | Other consumer | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and leases receivable				12
Consumer Portfolio Segment | Other consumer | Cumulative Effect, Period Of Adoption, Adjusted Balance
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and leases receivable				$ 1,174,187