Fair Value of Financial Instruments - (Schedule of Fair Value of Financial Instruments) (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014
ASSETS:
Cash and cash equivalents	$ 147,939	$ 166,092	$ 242,441	$ 256,979
Investment securities available-for-sale (at fair value)	1,046,047	1,157,246
Mortgage-backed securities-residential mortgage pass-through securities issued or guaranteed by U.S. Government agencies or sponsored enterprises held-to-maturity	381,172	427,503
Non-marketable securities	12,304	22,529
Loans held-for-sale	9,690	13,292
LIABILITIES:
Time deposits	1,174,098	1,193,883
Securities sold under agreements to repurchase	126,146	136,523
Federal Home Loan Bank advances	40,000	40,000
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)	274,242	310,978
Mortgage-backed securities-residential mortgage pass-through securities issued or guaranteed by U.S. Government agencies or sponsored enterprises held-to-maturity	302,852	340,131
Other Residential MBS Issued or Guaranteed by U.S. Government Agencies or Sponsored Enterprises [Member]
ASSETS:
Investment securities available-for-sale (at fair value)	766,194	845,543
Mortgage-backed securities-residential mortgage pass-through securities issued or guaranteed by U.S. Government agencies or sponsored enterprises held-to-maturity	78,320	87,372
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)	5,192
Carrying Amount [Member] | Level 1 [Member]
ASSETS:
Cash and cash equivalents	147,939	166,092
Carrying Amount [Member] | Level 2 [Member]
ASSETS:
Non-marketable securities	12,304	22,529
Loans held-for-sale	9,690	13,292
Accrued interest receivable	11,509	12,190
LIABILITIES:
Deposit transaction accounts	2,626,847	2,646,794
Time deposits	1,174,098	1,193,883
Securities sold under agreements to repurchase	126,146	136,523
Federal Home Loan Bank advances	40,000	40,000
Accrued interest payable	4,469	4,319
Carrying Amount [Member] | Level 3 [Member]
ASSETS:
Loans receivable, net	2,698,398	2,560,554
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)	274,242	310,978
Mortgage-backed securities-residential mortgage pass-through securities issued or guaranteed by U.S. Government agencies or sponsored enterprises held-to-maturity	302,852	340,131
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)	766,194	845,543
Mortgage-backed securities-residential mortgage pass-through securities issued or guaranteed by U.S. Government agencies or sponsored enterprises held-to-maturity	78,320	87,372
Carrying Amount [Member] | Other Securities [Member] | Level 3 [Member]
ASSETS:
Investment securities available-for-sale (at fair value)	419	419
Estimated Fair Value [Member] | Level 1 [Member]
ASSETS:
Cash and cash equivalents	147,939	166,092
Estimated Fair Value [Member] | Level 2 [Member]
ASSETS:
Non-marketable securities	12,304	22,529
Loans held-for-sale	9,690	13,292
Accrued interest receivable	11,509	12,190
LIABILITIES:
Deposit transaction accounts	2,626,847	2,646,794
Time deposits	1,174,828	1,182,098
Securities sold under agreements to repurchase	126,146	136,523
Federal Home Loan Bank advances	41,157	40,919
Accrued interest payable	4,469	4,319
Estimated Fair Value [Member] | Level 3 [Member]
ASSETS:
Loans receivable, net	2,811,598	2,613,381
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)	274,242	310,978
Mortgage-backed securities-residential mortgage pass-through securities issued or guaranteed by U.S. Government agencies or sponsored enterprises held-to-maturity	309,598	342,812
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)	766,194	845,543
Mortgage-backed securities-residential mortgage pass-through securities issued or guaranteed by U.S. Government agencies or sponsored enterprises held-to-maturity	78,507	85,773
Estimated Fair Value [Member] | Other Securities [Member] | Level 3 [Member]
ASSETS:
Investment securities available-for-sale (at fair value)	419	419
Interest rate swap derivatives [Member] | Carrying Amount [Member] | Level 2 [Member]
ASSETS:
Derivative asset	4,465	2,347
LIABILITIES:
Derivative liability	28,033	8,315
Interest rate swap derivatives [Member] | Estimated Fair Value [Member] | Level 2 [Member]
ASSETS:
Derivative asset	4,465	2,347
LIABILITIES:
Derivative liability	28,033	$ 8,315
Mortgage banking derivatives | Carrying Amount [Member] | Level 3 [Member]
ASSETS:
Derivative asset	414
LIABILITIES:
Derivative liability	178
Mortgage banking derivatives | Estimated Fair Value [Member] | Level 3 [Member]
ASSETS:
Derivative asset	414
LIABILITIES:
Derivative liability	$ 178