Business Combinations - Fair Value Estimates of Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Jul. 02, 2018	Jan. 16, 2018	Dec. 31, 2017
Liabilities
Gross loans receivable	$ 3,650,651			$ 2,845,712
Premier Merger
Assets
Cash and cash equivalents		$ 22,534
Interest earning deposits		3,309
Investment securities available for sale		4,493
Loans receivable		330,158
Other real estate owned		1,796
Premises and equipment, net		3,053
Federal Home Loan Bank stock, at cost		1,120
Bank owned life insurance		10,852
Accrued interest receivable		1,006
Prepaid expenses and other assets		1,603
Other intangible assets		7,075
Total assets acquired		386,999
Liabilities
Deposits		318,717
Federal Home Loan Bank advances		16,000
Securities sold under agreement to repurchase		462
Total liabilities acquired		5,935
Total liabilities acquired		341,114
Fair value of net assets acquired		45,885
Gross loans receivable		$ 335,400
Puget Sound Merger
Assets
Cash and cash equivalents			$ 25,889
Interest earning deposits			54,247
Investment securities available for sale			80,353
Loans receivable			388,462
Other real estate owned			0
Premises and equipment, net			732
Federal Home Loan Bank stock, at cost			623
Bank owned life insurance			6,264
Accrued interest receivable			1,448
Prepaid expenses and other assets			1,354
Other intangible assets			11,270
Total assets acquired			570,642
Liabilities
Deposits			505,885
Federal Home Loan Bank advances			0
Securities sold under agreement to repurchase			0
Total liabilities acquired			2,504
Total liabilities acquired			508,389
Fair value of net assets acquired			62,253
Gross loans receivable			$ 392,700