QUARTERLY FINANCIAL INFORMATION (UNAUDITED) (Details) $ / shares in Units, $ in Thousands		3 Months Ended																12 Months Ended
	Nov. 17, 2015	Jun. 30, 2016 USD ($) $ / shares		Mar. 31, 2016 USD ($) $ / shares		Dec. 31, 2015 USD ($) $ / shares		Sep. 30, 2015 USD ($) $ / shares		Jun. 30, 2015 USD ($) $ / shares		Mar. 31, 2015 USD ($) $ / shares		Dec. 31, 2014 USD ($) $ / shares		Sep. 30, 2014 USD ($) $ / shares		Jun. 30, 2016 USD ($) $ / shares		Jun. 30, 2015 USD ($) $ / shares		Jun. 30, 2014 USD ($) $ / shares
Quarterly Financial Information Disclosure [Abstract]
Interest and dividend income		$ 86,261		$ 84,282		$ 75,935		$ 71,229		$ 67,567		$ 62,911		$ 59,081		$ 54,805		$ 317,707		$ 244,364		$ 172,878
Interest expense		17,106		14,725		12,764		12,101		12,273		12,246		10,970		9,930		56,696		45,419		35,781
Net interest income		69,155		69,557		63,171		59,128		55,294		50,665		48,111		44,875		261,011		198,945		137,097
Provision for loan and lease losses		1,900		2,000		3,400		2,400		2,900		2,900		2,900		2,500		9,700		11,200		5,350
Net interest income, after provision for loan and lease losses		67,255		67,557		59,771		56,728		52,394		47,765		45,211		42,375		251,311		187,745		131,747
Non-interest income		17,015		23,316		16,220		9,789		10,278		8,366		6,697		5,249		66,340		30,590		22,455
Non-interest expense		32,985		29,408		27,445		22,918		20,752		20,343		18,937		17,446		112,756		77,478		59,933
INCOME BEFORE INCOME TAXES		51,285		61,465		48,546		43,599		41,920		35,788		32,971		30,178		204,895		140,857		94,269
Income tax expense		21,558		25,551		20,397		18,098		17,525		14,714		13,599		12,337		85,604		58,175		38,313
NET INCOME		29,727		35,914		28,149		25,501		24,395		21,074		19,372		17,841		119,291		82,682		55,956
Net income attributable to common stock		$ 29,650		$ 35,837		$ 28,071		$ 25,424		$ 24,318		$ 20,997		$ 19,294		$ 17,764		$ 118,982		$ 82,373		$ 55,647
Basic earnings per share (dollars per share) | $ / shares		$ 0.46	[1]	$ 0.56	[1]	$ 0.44	[1]	$ 0.40	[1]	$ 0.39	[1]	$ 0.34	[1]	$ 0.32	[1]	$ 0.30	[1]	$ 1.85	[2]	$ 1.35	[2],[3]	$ 0.97	[2],[3]
Diluted earnings per share (dollars per share) | $ / shares		$ 0.46	[1]	$ 0.56	[1]	$ 0.44	[1]	$ 0.40	[1]	$ 0.39	[1]	$ 0.34	[1]	$ 0.32	[1]	$ 0.30	[1]	$ 1.85	[2]	$ 1.34	[2],[3]	$ 0.96	[2],[3]
Common stock split, conversion ratio	4

[1] Common stock amounts have been retroactively restated for all prior periods presented to reflect the four-for-one forward split of the Company’s common stock effected in the form of a stock dividend that was distributed on November 17, 2015.

[2] Amounts have been retroactively restated for all prior periods presented to reflect the four-for-one forward split of the Company’s common stock effected in the form of a stock dividend that was distributed on November 17, 2015

[3] Common stock amounts have been retroactively restated for all prior periods presented to reflect the four-for-one forward split of the Company’s common stock effected in the form of a stock dividend that was distributed on November 17, 2015.