CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss, Net of Deferred Taxes [Member]	Unallocated Common Stock of Employee Stock Ownership Plan ("ESOP") [Member]	Unearned Restricted Stock Award Common Stock [Member]	Common Stock Held by BMP [Member]	Treasury Stock, at Cost [Member]	Total
Balance at Dec. 31, 2014	$ 529	$ 254,358	$ 427,126	$ (8,547)	$ (2,545)	$ (3,066)	$ (9,164)	$ (198,966)	$ 459,725
Balance (in shares) at Dec. 31, 2014	36,855,019
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	$ 0	0	44,772	0	0	0	0	0	44,772
Other comprehensive income (loss), net of tax	0	0	0	(254)	0	0	0	0	(254)
Exercise of stock options, net expired options	$ 4	6,809	0	0	0	0	0	0	6,813
Exercise of stock options, net expired options (in shares)	455,310
Release of shares, net of forfeitures	$ 0	526	0	0	0	(1,061)	(190)	1,015	290
Release of shares, net of forfeitures (in shares)	81,663
Stock-based compensation	$ 0	1,105	0	0	232	1,856	0	0	3,193
Cash dividends declared and paid	0	0	(20,292)	0	0	0	0	0	(20,292)
Repurchase of common stock	$ 0	0	0	0	0	0	0	(300)	(300)
Repurchase of common stock (in shares)	(20,000)
Balance at Dec. 31, 2015	$ 533	262,798	451,606	(8,801)	(2,313)	(2,271)	(9,354)	(198,251)	493,947
Balance (in shares) at Dec. 31, 2015	37,371,992
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	$ 0	0	72,514	0	0	0	0	0	72,514
Other comprehensive income (loss), net of tax	0	0	0	2,862	0	0	0	0	2,862
Exercise of stock options, net expired options	$ 3	3,567	0	0	0	0	0	0	3,570
Exercise of stock options, net expired options (in shares)	245,992
Release of shares, net of forfeitures	$ 0	659	0	0	0	(780)	(222)	708	365
Release of shares, net of forfeitures (in shares)	85,137
Stock-based compensation	$ 0	1,276	0	0	231	1,119	0	349	2,975
Shares received to satisfy distribution of retirement benefits	$ 0	(2,717)	0	0	0	0	2,717	(1,820)	(1,820)
Shares received to satisfy distribution of retirement benefits (in shares)	(107,008)
Tax benefit from market valuation adjustment on distribution of BMP ESOP shares	$ 0	717	0	0	0	0	0	0	717
ESOP Share Acquisition Loan payoff	$ 0	12,056	0	0	2,082	0	0	(2,819)	11,319
ESOP Share Acquisition Loan Payoff (in shares)	(140,260)
Cash dividends declared and paid	$ 0	0	(21,581)	0	0	0	0	0	(20,581)
Balance at Dec. 31, 2016	$ 536	278,356	503,539	(5,939)	0	(1,932)	(6,859)	(201,833)	565,868
Balance (in shares) at Dec. 31, 2016	37,455,853
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	$ 0	0	51,882	0	0	0	0	0	51,882
Other comprehensive income (loss), net of tax	0	0	0	3,011	0	0	0	0	3,011
Exercise of stock options, net expired options	$ 0	792	0	0	0	0	0	0	792
Exercise of stock options, net expired options (in shares)	51,708
Release of shares, net of forfeitures	$ 0	1,269	0	0	0	(2,649)	(170)	1,786	236
Release of shares, net of forfeitures (in shares)	141,867
Stock-based compensation	$ 0	0	0	0	0	1,687	0	0	1,687
Shares received to satisfy distribution of retirement benefits	$ 0	(3,687)	0	0	0	0	4,293	(4,511)	(3,905)
Shares received to satisfy distribution of retirement benefits (in shares)	(230,358)
Reclassification of tax effects on other comprehensive income	$ 0	0	713	(713)	0	0	0	0	0
Cash dividends declared and paid	0	0	(21,004)	0	0	0	0	0	(21,004)
Balance at Dec. 31, 2017	$ 536	$ 276,730	$ 535,130	$ (3,641)	$ 0	$ (2,894)	$ (2,736)	$ (204,558)	$ 598,567
Balance (in shares) at Dec. 31, 2017	37,419,070