Fair Value - Carrying Amounts and Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Assets
Securities available-for-sale	$ 391,852	$ 306,589
Securities held-to-maturity	394,292	318,748
Liabilities
Subordinated Debt.	39,183
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Cash and cash equivalents	316,222	266,103
Significant Other Observable Inputs (Level 2)
Assets
Securities available-for-sale	391,852	306,589
Securities held-to-maturity	394,292	318,748
Loans (including loans held-for-sale), net	3,419	5,705
Accrued interest receivable	2,423	1,961
I/O strips receivables	968	1,067
Liabilities
Time deposits	194,844	225,047
Other deposits	2,288,428	2,037,423
Subordinated Debt.	40,384
Accrued interest payable	389	168
Significant Unobservable Inputs (Level 3)
Assets
Loans (including loans held-for-sale), net	1,507,967	1,444,076
Accrued interest receivable	5,562	4,898
Carrying amount
Assets
Cash and cash equivalents	316,222	266,103
Securities available-for-sale	391,852	306,589
Securities held-to-maturity	398,341	324,010
Loans (including loans held-for-sale), net	1,566,428	1,489,223
FHLB and FRB stock and other investments	17,911	15,196
Accrued interest receivable	7,985	6,859
I/O strips receivables	968	1,067
Liabilities
Time deposits	194,561	224,717
Other deposits	2,288,428	2,037,423
Subordinated Debt.	39,183
Accrued interest payable	389	168
Carried at fair value
Assets
Cash and cash equivalents	316,222	266,103
Securities available-for-sale	391,852	306,589
Securities held-to-maturity	394,292	318,748
Loans (including loans held-for-sale), net	1,511,386	1,449,781
Accrued interest receivable	7,985	6,859
I/O strips receivables	968	1,067
Liabilities
Time deposits	194,844	225,047
Other deposits	2,288,428	2,037,423
Subordinated Debt.	40,384
Accrued interest payable	$ 389	$ 168