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 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	33,388	0	0	0	0	0	$ 33,388
Other comprehensive income (loss), net of tax	0	0	0	(626)	0	0	0	0	(626)
Exercise of stock options, net of expired options	3	4,053	0	0	0	0	0	0	$ 4,056
Exercise of stock options, net of expired options (in shares)									274,355
Release of shares, net of forfeitures	0	680	0	0	0	(1,061)	(190)	988	$ 417
Release of shares, net of forfeitures (in shares)									79,500
Stock-based compensation	0	815	0	0	174	1,418	0	0	$ 2,407
Cash dividends declared and paid	0	0	(15,188)	0	0	0	0	0	(15,188)
Repurchase of common stock	0	0	0	0	0	0	0	(300)	$ (300)
Repurchase of common stock (in shares)									(20,000)
Balance at Sep. 30, 2015	532	259,906	445,326	(9,173)	(2,371)	(2,709)	(9,354)	(198,278)	$ 483,879
Balance (in shares) at Sep. 30, 2015									37,188,874
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
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
Exercise of stock options, net of expired options	2	2,735	0	0	0	0	0	0	$ 2,737
Exercise of stock options, net of expired options (in shares)									193,828
Release of shares, net of forfeitures	0	714	0	0	0	(807)	(222)	707	$ 392
Release of shares, net of forfeitures (in shares)									85,040
Stock-based compensation	0	980	0	0	173	775	0	349	$ 2,277
Cash dividends declared and paid	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