CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (USD $) In Thousands, except Share data, unless otherwise specified	Total USD ($)	Common Stock and Paid in Capital [Member] USD ($)	Retained Earnings (Accumulated Deficit) [Member] USD ($)	Common Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member] USD ($)	Unearned Restricted ESOP Shares [Member] USD ($)
Balance, beginning of the period at Dec. 31, 2013	$ 538,331	$ 569,028	$ (25,714)		$ (2,996)	$ (1,987)
Balance, beginning of the period (in shares) at Dec. 31, 2013		19,543,769
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	54,070		54,070
Other comprehensive income, net of income tax	2,738				2,738
Accrual of dividends on common stock	(14,092)		(14,092)
Stock Redeemed or Called During Period, Shares				(34,340)
Stock Redeemed or Called During Period, Value	0	(1,987)				1,987
Stock Repurchased and Retired During Period, Shares				(13,550)
Stock Repurchased and Retired During Period, Value	(555)	(555)
Proceeds from issuance of common stock for stockholder reinvestment program (in shares)		3,170
Proceeds from issuance of common stock for stockholder reinvestment program	127	127
Issuance of restricted stock and amortization of related compensation (in shares)		72,499
Issuance of restricted stock and recognition of share-based compensation	2,269	2,269
Balance, end of the period at Dec. 31, 2014	582,888	568,882	14,264		(258)	0
Balance, end of the period (in shares) at Dec. 31, 2014		19,571,548
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	12,134		12,134
Other comprehensive income, net of income tax	1,395				1,395
Accrual of dividends on common stock	(3,775)		(3,775)
Proceeds from issuance of common stock for stockholder reinvestment program (in shares)		84,429
Proceeds from issuance of common stock for stockholder reinvestment program	538	538
Issuance of restricted stock and amortization of related compensation (in shares)		810
Issuance of restricted stock and recognition of share-based compensation	33	33
Stock Issued During Period, Shares, Acquisitions	1,319,854
Stock Issued During Period, Value, Acquisitions	58,100	58,100
Balance, end of the period at Mar. 31, 2015	$ 651,313	$ 627,553	$ 22,623		$ 1,137	$ 0
Balance, end of the period (in shares) at Mar. 31, 2015		20,976,641