Investment Securities - The amortized cost and estimated fair value of securities (Details)	3 Months Ended	6 Months Ended	12 Months Ended
	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2016 USD ($) purchase_agreement	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Available-for-sale:
Amortized Cost		$ 385,662,000	$ 385,662,000	$ 279,711,000
Unrealized Gain		804,000	804,000	1,953,000
Unrealized Loss		(5,503,000)	(5,503,000)	(1,391,000)
Estimated Fair Value		380,963,000	380,963,000	280,273,000
Held-to-maturity:
Amortized Cost		8,565,000	8,565,000	9,642,000
Unrealized Gain		0	0	0
Unrealized Loss		(104,000)	(104,000)	(70,000)
Estimated Fair Value		8,461,000	8,461,000	9,572,000
Total securities
Amortized Cost		394,227,000	394,227,000	289,353,000
Unrealized Gain		804,000	804,000	1,953,000
Unrealized Loss		(5,607,000)	(5,607,000)	(1,461,000)
Estimated Fair Value		389,424,000	$ 389,424,000	289,845,000
Additional disclosures
Number of inverse putable reverse repurchase of the Bank's secured by collateral | purchase_agreement			3
Value of inverse putable reverse repurchases secured by collateral		28,500,000	$ 28,500,000
OTTI realized		2,000	205,000
Other-than-temporary-impairment loss on investment securities			(205,000)	0	$ (29,000)
Gross gains			1,806,000	300,000	2,100,000
Gross losses			(9,000)	(27,000)	(578,000)
Net proceeds from the sale of available-for-sale securities			223,365,000	22,032,000	163,241,000
Net Proceeds from the maturity/call of available-for-sale securities			7,580,000	5,610,000	$ 3,100,000
CRA
Available-for-sale:
Estimated Fair Value	$ 500,000
Additional disclosures
OTTI realized	207,000
CRA investment purchased, par value	$ 50
Mortgage-backed securities: residential
Additional disclosures
Estimated par value of securities pledged as collateral for the Bank's inverse putable reverse repurchases		63,600,000	63,600,000
Fair value of securities pledged as collateral for the Bank's inverse putable reverse repurchases		65,300,000	65,300,000
Home Owners Association Loans
Additional disclosures
Value of inverse putable reverse repurchases secured by collateral		21,500,000	21,500,000
Corporate
Available-for-sale:
Amortized Cost		37,475,000	37,475,000
Unrealized Gain		372,000	372,000
Unrealized Loss		(205,000)	(205,000)
Estimated Fair Value		37,642,000	37,642,000
Municipal bonds
Available-for-sale:
Amortized Cost		120,155,000	120,155,000	128,546,000
Unrealized Gain		338,000	338,000	1,796,000
Unrealized Loss		(1,690,000)	(1,690,000)	(97,000)
Estimated Fair Value		118,803,000	118,803,000	130,245,000
Collateralized mortgage obligation: residential
Available-for-sale:
Amortized Cost		31,536,000	31,536,000	24,722,000
Unrealized Gain		25,000	25,000	4,000
Unrealized Loss		(173,000)	(173,000)	(183,000)
Estimated Fair Value		31,388,000	31,388,000	24,543,000
Mortgage-backed securities: residential
Available-for-sale:
Amortized Cost		196,496,000	196,496,000	126,443,000
Unrealized Gain		69,000	69,000	153,000
Unrealized Loss		(3,435,000)	(3,435,000)	(1,111,000)
Estimated Fair Value		193,130,000	193,130,000	125,485,000
Held-to-maturity:
Amortized Cost		7,375,000	7,375,000	8,400,000
Unrealized Gain		0	0	0
Unrealized Loss		(104,000)	(104,000)	(70,000)
Estimated Fair Value		7,271,000	7,271,000	8,330,000
Other
Held-to-maturity:
Amortized Cost		1,190,000	1,190,000	1,242,000
Unrealized Gain		0	0	0
Unrealized Loss		0	0	0
Estimated Fair Value		$ 1,190,000	$ 1,190,000	$ 1,242,000