Fair Value of Financial Instruments - (Schedule of Fair Value of Financial Instruments) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
ASSETS:
Cash and cash equivalents	$ 286,870	$ 257,364
Investment securities available-for-sale (at fair value)	917,865	855,345
Mortgage-backed securities-residential mortgage pass-through securities issued or guaranteed by U.S. Government agencies or sponsored enterprises held-to-maturity	283,369	258,730
Non-marketable securities	14,088	15,030
Loans held-for-sale	51,050	4,629
LIABILITIES:
Time deposits	1,147,452	1,118,050
Securities sold under agreements to repurchase	141,187	130,463
Federal Home Loan Bank advances	77,335	129,115
Residential Mortgage Pass-Through Securities Issued or Guaranteed by U.S. Government Agencies or Sponsored Enterprises [Member]
ASSETS:
Investment securities available-for-sale (at fair value)	188,630	168,648
Mortgage-backed securities-residential mortgage pass-through securities issued or guaranteed by U.S. Government agencies or sponsored enterprises held-to-maturity	191,136	204,352
Other Residential MBS Issued or Guaranteed by U.S. Government Agencies or Sponsored Enterprises [Member]
ASSETS:
Investment securities available-for-sale (at fair value)	727,729	685,230
Mortgage-backed securities-residential mortgage pass-through securities issued or guaranteed by U.S. Government agencies or sponsored enterprises held-to-maturity	92,233	54,378
Other Securities [Member]
ASSETS:
Investment securities available-for-sale (at fair value)	469	419
Municipal [Member]
ASSETS:
Investment securities available-for-sale (at fair value)	1,037	1,048
Carrying Amount [Member] | Level 1 [Member]
ASSETS:
Cash and cash equivalents	286,870	257,364
Carrying Amount [Member] | Level 2 [Member]
ASSETS:
Non-marketable securities	14,088	15,030
Loans held-for-sale	51,050	4,629
Accrued interest receivable	18,343	14,255
LIABILITIES:
Deposit transaction accounts	3,561,858	2,861,509
Time deposits	1,147,452	1,118,050
Securities sold under agreements to repurchase	141,187	130,463
Federal Home Loan Bank advances	77,335	129,115
Accrued interest payable	7,198	5,776
Carrying Amount [Member] | Level 3 [Member]
ASSETS:
Loans receivable, net	3,702,334	3,178,947
Carrying Amount [Member] | Residential Mortgage Pass-Through Securities Issued or Guaranteed by U.S. Government Agencies or Sponsored Enterprises [Member] | Level 2 [Member]
ASSETS:
Investment securities available-for-sale (at fair value)	188,630	168,648
Mortgage-backed securities-residential mortgage pass-through securities issued or guaranteed by U.S. Government agencies or sponsored enterprises held-to-maturity	191,136	204,352
Carrying Amount [Member] | Other Residential MBS Issued or Guaranteed by U.S. Government Agencies or Sponsored Enterprises [Member] | Level 2 [Member]
ASSETS:
Investment securities available-for-sale (at fair value)	727,729	685,230
Mortgage-backed securities-residential mortgage pass-through securities issued or guaranteed by U.S. Government agencies or sponsored enterprises held-to-maturity	92,233	54,378
Carrying Amount [Member] | Other Securities [Member] | Level 3 [Member]
ASSETS:
Investment securities available-for-sale (at fair value)	469	419
Carrying Amount [Member] | Municipal [Member] | Level 2 [Member]
ASSETS:
Municipal obligations	818	829
Carrying Amount [Member] | Municipal [Member] | Level 3 [Member]
ASSETS:
Municipal obligations	219	219
Estimated Fair Value [Member] | Level 1 [Member]
ASSETS:
Cash and cash equivalents	286,870	257,364
Estimated Fair Value [Member] | Level 2 [Member]
ASSETS:
Non-marketable securities	14,088	15,030
Loans held-for-sale	51,050	4,629
Accrued interest receivable	18,343	14,255
LIABILITIES:
Deposit transaction accounts	3,561,858	2,861,509
Time deposits	1,147,452	1,118,050
Securities sold under agreements to repurchase	141,187	130,463
Federal Home Loan Bank advances	77,647	130,300
Accrued interest payable	7,198	5,776
Estimated Fair Value [Member] | Level 3 [Member]
ASSETS:
Loans receivable, net	3,670,007	3,167,508
Estimated Fair Value [Member] | Residential Mortgage Pass-Through Securities Issued or Guaranteed by U.S. Government Agencies or Sponsored Enterprises [Member] | Level 2 [Member]
ASSETS:
Investment securities available-for-sale (at fair value)	188,630	168,648
Mortgage-backed securities-residential mortgage pass-through securities issued or guaranteed by U.S. Government agencies or sponsored enterprises held-to-maturity	188,609	204,048
Estimated Fair Value [Member] | Other Residential MBS Issued or Guaranteed by U.S. Government Agencies or Sponsored Enterprises [Member] | Level 2 [Member]
ASSETS:
Investment securities available-for-sale (at fair value)	727,729	685,230
Mortgage-backed securities-residential mortgage pass-through securities issued or guaranteed by U.S. Government agencies or sponsored enterprises held-to-maturity	90,107	52,723
Estimated Fair Value [Member] | Other Securities [Member] | Level 3 [Member]
ASSETS:
Investment securities available-for-sale (at fair value)	469	419
Estimated Fair Value [Member] | Municipal [Member] | Level 2 [Member]
ASSETS:
Municipal obligations	818	829
Estimated Fair Value [Member] | Municipal [Member] | Level 3 [Member]
ASSETS:
Municipal obligations	219	219
Interest rate swap derivatives [Member] | Carrying Amount [Member] | Level 2 [Member]
ASSETS:
Derivative asset	24,695	12,972
LIABILITIES:
Derivative liability	3,300	3,751
Interest rate swap derivatives [Member] | Estimated Fair Value [Member] | Level 2 [Member]
ASSETS:
Derivative asset	24,695	12,972
LIABILITIES:
Derivative liability	3,300	3,751
Mortgage banking derivatives | Carrying Amount [Member] | Level 3 [Member]
ASSETS:
Derivative asset	1,316	133
LIABILITIES:
Derivative liability	601	7
Mortgage banking derivatives | Estimated Fair Value [Member] | Level 3 [Member]
ASSETS:
Derivative asset	1,316	133
LIABILITIES:
Derivative liability	$ 601	$ 7