Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Additional Paid-in Capital	Retained Earnings (Deficit)	Treasury Stock	Accumulated Other Comprehensive Income (Loss)	Class A	Class A Common Stock	Class B	Class B Common Stock
Beginning Balance, shares at Dec. 31, 2016							40,969,097		188,474
Beginning Balance at Dec. 31, 2016	$ 982,441	$ 875,314	$ 188,451	$ (77,373)	$ (3,995)		$ 44		$ 0
Net income	38,989		38,989
Exchange of B shares to A shares, shares							188,474		(188,474)
Exchange of B shares to A shares							$ 0		$ 0
Stock-based compensation and warrant expense	1,431	1,431
Stock issued in connection with equity awards and warrants, shares							1,265,015
Stock issued in connection with equity awards and warrants	21,665	21,664					$ 1
Other	(15)	(15)
Other comprehensive income (loss)	10,736				10,736
Ending Balance, shares at Mar. 31, 2017							42,422,586		0
Ending Balance at Mar. 31, 2017	1,055,247	898,394	227,440	(77,373)	6,741		$ 45		$ 0
Cumulative adjustment from adoption of new accounting standards (1)			(725)		725
Cumulative adjustment from adoption of new accounting standards (1) | ASU 2016-01			1,000
Cumulative adjustment from adoption of new accounting standards (1) | ASU 2018-02			(1,700)
Beginning Balance, shares at Dec. 31, 2017						44,371,104	44,371,104	0	0
Beginning Balance at Dec. 31, 2017	1,179,172	933,960	313,645	(77,373)	8,893		$ 47		$ 0
Net income	40,099		40,099
Stock issued in connection with acquisition, net of issuance cost, shares							1,754,362
Stock issued in connection with acquisition	94,122	94,120					$ 2
Stock-based compensation and warrant expense	1,871	1,871
Stock issued in connection with equity awards and warrants, shares							569,184
Stock issued in connection with equity awards and warrants	7,084	7,084					$ 0
Shares surrendered for tax withholding obligations, shares							(40,647)
Shares surrendered for tax withholding obligations	(2,066)	(2,066)
Other	(282)	(282)
Other comprehensive income (loss)	(15,133)
Other comprehensive income (loss) | ASU 2016-01 and 2018-02	(15,858)				(15,858)
Ending Balance, shares at Mar. 31, 2018						46,620,627	46,654,003	0	0
Ending Balance at Mar. 31, 2018	$ 1,304,142	$ 1,034,687	$ 353,019	$ (77,373)	$ (6,240)		$ 49		$ 0