Condensed Consolidated Statements of Stockholders' Equity (USD $) In Thousands	Total	Common Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]
Beginning balance at Dec. 31, 2013	$ 771,887us-gaap_StockholdersEquity	$ 491,068	$ 290,149	$ (9,330)
Beginning balance, shares at Dec. 31, 2013		105,370
Repurchase of common stock	(32)	(32)
Repurchase of common stock, shares		(2)
Exercise of stock options	3,684	3,684
Exercise of stock options, shares		334
Tax benefit from exercise of stock options	559	559
Shares issued pursuant to stock-based compensation plan	656	656
Shares issued pursuant to stock-based compensation plan, shares		310
Cash dividends declared on common stock	(10,608)us-gaap_DividendsCommonStockCash		(10,608)
Net earnings	28,661us-gaap_NetIncomeLoss		28,661
Other comprehensive income	14,374			14,374
Ending balance at Mar. 31, 2014	809,181us-gaap_StockholdersEquity	495,935	308,202	5,044
Ending balance, shares at Mar. 31, 2014		106,012
Beginning balance at Dec. 31, 2014	878,109us-gaap_StockholdersEquity	495,220	351,814	31,075
Beginning balance, shares at Dec. 31, 2014		105,893
Repurchase of common stock	(497)	(497)
Repurchase of common stock, shares		(32)
Exercise of stock options	3,313	3,313
Exercise of stock options, shares		306
Tax benefit from exercise of stock options	614	614
Shares issued pursuant to stock-based compensation plan	732	732
Shares issued pursuant to stock-based compensation plan, shares		80
Cash dividends declared on common stock	(12,742)us-gaap_DividendsCommonStockCash		(12,742)
Net earnings	15,833us-gaap_NetIncomeLoss		15,833
Other comprehensive income	11,756			11,756
Ending balance at Mar. 31, 2015	$ 897,118us-gaap_StockholdersEquity	$ 499,382	$ 354,905	$ 42,831
Ending balance, shares at Mar. 31, 2015		106,247

Amount of increase in additional paid in capital (APIC) resulting from a tax benefit associated with share-based compensation plan other than an employee stock ownership plan (ESOP). Includes, but is not limited to, excess tax benefit.

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