Fair Value of Financial Instruments - (Schedule of Fair Value of Financial Instruments) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
ASSETS:
Cash and cash equivalents	$ 241,160	$ 152,736	$ 124,977	$ 166,092
Investment securities available-for-sale (at fair value)	812,051	884,232
Mortgage-backed securities-residential mortgage pass-through securities issued or guaranteed by U.S. Government agencies or sponsored enterprises held-to-maturity	275,370	332,505
Non-marketable securities	15,537	14,949
Loans held-for-sale	12,212	24,187
LIABILITIES:
Time deposits	1,133,167	1,172,046
Securities sold under agreements to repurchase	92,814	92,011
Federal Home Loan Bank advances	129,115	38,665
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)	181,389	227,160
Mortgage-backed securities-residential mortgage pass-through securities issued or guaranteed by U.S. Government agencies or sponsored enterprises held-to-maturity	217,431	263,411
Other Residential MBS Issued or Guaranteed by U.S. Government Agencies or Sponsored Enterprises [Member]
ASSETS:
Investment securities available-for-sale (at fair value)	628,479	652,739
Mortgage-backed securities-residential mortgage pass-through securities issued or guaranteed by U.S. Government agencies or sponsored enterprises held-to-maturity	57,939	69,094
Other Securities [Member]
ASSETS:
Investment securities available-for-sale (at fair value)	419	419
Municipal [Member]
ASSETS:
Investment securities available-for-sale (at fair value)	1,764	3,914
Carrying Amount [Member] | Level 1 [Member]
ASSETS:
Cash and cash equivalents	241,160	152,736
Carrying Amount [Member] | Level 2 [Member]
ASSETS:
Non-marketable securities	15,537	14,949
Loans held-for-sale	12,212	24,187
Accrued interest receivable	16,042	12,562
LIABILITIES:
Deposit transaction accounts	2,813,175	2,696,603
Time deposits	1,133,167	1,172,046
Securities sold under agreements to repurchase	92,814	92,011
Federal Home Loan Bank advances	129,115	38,665
Accrued interest payable	6,676	4,973
Carrying Amount [Member] | Level 3 [Member]
ASSETS:
Loans receivable, net	3,120,543	2,860,921
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)	181,389	227,160
Mortgage-backed securities-residential mortgage pass-through securities issued or guaranteed by U.S. Government agencies or sponsored enterprises held-to-maturity	217,431	263,411
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)	628,479	652,739
Mortgage-backed securities-residential mortgage pass-through securities issued or guaranteed by U.S. Government agencies or sponsored enterprises held-to-maturity	57,939	69,094
Carrying Amount [Member] | Other Securities [Member] | Level 3 [Member]
ASSETS:
Investment securities available-for-sale (at fair value)	419	419
Carrying Amount [Member] | Municipal [Member] | Level 2 [Member]
ASSETS:
Municipal obligations	1,499	3,648
Carrying Amount [Member] | Municipal [Member] | Level 3 [Member]
ASSETS:
Municipal obligations	265	265
Estimated Fair Value [Member] | Level 1 [Member]
ASSETS:
Cash and cash equivalents	241,160	152,736
Estimated Fair Value [Member] | Level 2 [Member]
ASSETS:
Non-marketable securities	15,537	14,949
Loans held-for-sale	12,212	24,187
Accrued interest receivable	16,042	12,562
LIABILITIES:
Deposit transaction accounts	2,813,175	2,696,603
Time deposits	1,133,167	1,172,046
Securities sold under agreements to repurchase	92,814	92,011
Federal Home Loan Bank advances	130,300	39,324
Accrued interest payable	6,676	4,973
Estimated Fair Value [Member] | Level 3 [Member]
ASSETS:
Loans receivable, net	3,117,549	2,879,860
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)	181,389	227,160
Mortgage-backed securities-residential mortgage pass-through securities issued or guaranteed by U.S. Government agencies or sponsored enterprises held-to-maturity	218,786	264,862
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)	628,479	652,739
Mortgage-backed securities-residential mortgage pass-through securities issued or guaranteed by U.S. Government agencies or sponsored enterprises held-to-maturity	56,822	67,711
Estimated Fair Value [Member] | Other Securities [Member] | Level 3 [Member]
ASSETS:
Investment securities available-for-sale (at fair value)	419	419
Estimated Fair Value [Member] | Municipal [Member] | Level 2 [Member]
ASSETS:
Municipal obligations	1,499	3,648
Estimated Fair Value [Member] | Municipal [Member] | Level 3 [Member]
ASSETS:
Municipal obligations	265	265
Interest rate swap derivatives [Member] | Carrying Amount [Member] | Level 2 [Member]
ASSETS:
Derivative asset	11,179	11,428
LIABILITIES:
Derivative liability	5,418	3,279
Interest rate swap derivatives [Member] | Estimated Fair Value [Member] | Level 2 [Member]
ASSETS:
Derivative asset	11,179	11,428
LIABILITIES:
Derivative liability	5,418	3,279
Mortgage banking derivatives | Carrying Amount [Member] | Level 3 [Member]
ASSETS:
Derivative asset	233	287
LIABILITIES:
Derivative liability	9	187
Mortgage banking derivatives | Estimated Fair Value [Member] | Level 3 [Member]
ASSETS:
Derivative asset	233	287
LIABILITIES:
Derivative liability	$ 9	$ 187