CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock [Member]	Common Stock and Paid in Capital [Member]	Retained Earnings (Accumulated Deficit) [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Balance, beginning of the period (in shares) at Dec. 31, 2014		19,571,548
Balance, beginning of the period at Dec. 31, 2014	$ 582,888		$ 568,882	$ 14,264	$ (258)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	45,222			45,222
Other comprehensive income, net of income tax	(472)				(472)
Accrual of dividends on common stock	(19,871)			(19,871)
Proceeds from issuance of common stock for stockholder reinvestment program (in shares)		810
Proceeds from issuance of common stock for stockholder reinvestment program	34		34
Issuance of restricted stock, net, and recognition of share-based compensation (in shares)		120,043
Issuance of restricted stock, net, and recognition of share-based compensation	$ 3,088		3,088
Issuance of shares for acquisitions (in shares)	14,549,854
Issuance of shares for acquisitions	$ 688,773		688,773
Excess tax benefit on stock-based compensation	397		397
Balance, end of the period (in shares) at Dec. 31, 2015		34,242,255
Balance, end of the period at Dec. 31, 2015	1,300,059		1,261,174	39,615	(730)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	62,581			62,581
Other comprehensive income, net of income tax	8,743				8,743
Accrual of dividends on common stock	$ (22,143)			(22,143)
Repurchase of common stock under the terms of the repurchase plan (in shares)	484,350
Repurchase of common stock under the terms of the repurchase plan	$ (21,098)
Issuance of restricted stock, net, and recognition of share-based compensation (in shares)		109,406
Issuance of restricted stock, net, and recognition of share-based compensation	3,129		3,129
Balance, end of the period (in shares) at Sep. 30, 2016		33,867,311
Balance, end of the period at Sep. 30, 2016	$ 1,331,271		$ 1,243,205	$ 80,053	$ 8,013