Quarterly Financial Results (unaudited) (Details) - USD ($)	3 Months Ended												12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Results (unaudited) [Abstract]
Interest income	$ 101,493,000	$ 97,380,000	$ 83,762,000	$ 80,974,000	$ 77,797,000	$ 67,192,000	$ 55,503,000	$ 54,679,000	$ 53,533,000	$ 52,782,000	$ 50,564,000	$ 49,291,000	$ 363,608,928	$ 255,169,880	$ 206,169,962
Net interest income	89,413,000	86,635,000	75,044,000	73,902,000	71,475,000	62,059,000	51,831,000	51,269,000	50,313,000	49,537,000	47,226,000	45,908,000	306,666,223	227,444,418	189,349,889
Provision for loan losses	3,046,000	6,108,000	5,280,000	3,894,000	5,459,000	2,228,000	1,186,000	315,000	2,041,000	851,000	254,000	488,000	18,328,058	9,188,497	3,634,660
Net income before taxes	54,345,000	48,693,000	46,546,000	41,800,000	40,432,000	36,134,000	33,917,000	32,617,000	28,264,000	27,215,000	25,668,000	24,506,000	191,383,862	143,097,930	105,652,684
Net income	36,097,000	32,377,000	30,787,000	27,964,000	26,854,000	24,149,000	22,665,000	21,843,000	18,737,000	18,197,000	17,170,000	16,367,000	127,224,695	95,509,402	70,471,167
Net income available to common stockholders	$ 36,097,000	$ 32,377,000	$ 30,787,000	$ 27,964,000	$ 26,854,000	$ 24,149,000	$ 22,665,000	$ 21,843,000	$ 18,737,000	$ 18,197,000	$ 17,170,000	$ 16,367,000	$ 127,224,695	$ 95,509,402	$ 70,471,167
Basic net income per common share (in dollars per share)	$ 0.79	$ 0.71	$ 0.75	$ 0.70	$ 0.67	$ 0.64	$ 0.65	$ 0.62	$ 0.54	$ 0.52	$ 0.49	$ 0.47	$ 2.96	$ 2.58	$ 2.03
Diluted net income per common share (in dollars per share)	$ 0.78	$ 0.71	$ 0.73	$ 0.68	$ 0.65	$ 0.62	$ 0.64	$ 0.62	$ 0.53	$ 0.52	$ 0.49	$ 0.47	$ 2.91	$ 2.52	$ 2.01