CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (UNAUDITED) - 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 ESOP [Member]	Unearned Stock Award Common Stock [Member]	Common Stock Held by BMP [Member]	Treasury Stock, at Cost [Member]	Total
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	71,782	0	0	0	0	0	71,782
Other comprehensive income (loss), net of tax	0	0	0	691	0	0	0	0	691
Exercise of stock options, net of expired options	$ 2	2,799	0	0	0	0	0	0	2,801
Exercise of stock options, net of expired options (in shares)	193,828
Release of shares, net of forfeitures	$ 0	650	0	0	0	(807)	(222)	707	328
Release of shares, net of forfeitures (in shares)	85,040
Stock-based compensation	$ 0	980	0	0	173	775	0	349	2,277
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 ESOP shares	$ 0	717	0	0	0	0	0	0	717
Cash dividends declared and paid, net	0	0	(15,432)	0	0	0	0	0	(15,432)
Balance at Sep. 30, 2016	$ 535	265,227	507,956	(8,110)	(2,140)	(2,303)	(6,859)	(199,015)	555,291
Balance (in shares) at Sep. 30, 2016	37,543,852
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	36,459	0	0	0	0	0	36,459
Other comprehensive income (loss), net of tax	0	0	0	1,228	0	0	0	0	1,228
Exercise of stock options, net of expired options	$ 0	680	0	0	0	0	0	0	680
Exercise of stock options, net of expired options (in shares)	45,174
Release of shares, net of forfeitures	$ 0	1,325	0	0	0	(2,874)	(170)	1,917	198
Release of shares, net of forfeitures (in shares)	152,215
Stock-based compensation	$ 0	0	0	0	0	1,270	0	0	1,270
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)
Cash dividends declared and paid, net	$ 0	0	(15,761)	0	0	0	0	0	(15,761)
Balance at Sep. 30, 2017	$ 536	$ 276,674	$ 524,237	$ (4,711)	$ 0	$ (3,536)	$ (2,736)	$ (204,427)	$ 586,037
Balance (in shares) at Sep. 30, 2017	37,422,884