CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDER'S EQUITY - USD ($) $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings
Balance Beginning of Period, Shares (in shares) at Dec. 31, 2016		77,666,000
Balance, Beginning of Period at Dec. 31, 2016	$ 839,667	$ 777	$ (123,051)	$ 798,652	$ (57,154)	$ 220,443
Balance, Beginning of Period, Treasury Stock, shares (in shares) at Dec. 31, 2016			(2,946,000)
Net income	6,394					6,394
Other comprehensive income (loss), net of tax	5,701				5,701
Issuance of common stock (in shares)		132,000
Issuance of common stock	1	$ 1
Issuance of common stock through employee stock purchase plan (in shares)		12,000
Issuance of common stock through employee stock purchase plan	509			509
Issuance of common stock for vesting of share based awards, net of shares withheld for taxes (in shares)		(161,000)
Issuance of common stock for vesting of share based awards, net of shares withheld for taxes	(5,470)	$ 1		(5,471)
Share-based compensation	5,688			5,688
Exercise of warrants (in shares)		214,000
Exercise of warrants	1	$ 3		(2)
Balance End of Period, Shares (in shares) at Mar. 31, 2017		78,185,000
Balance, End of Period at Mar. 31, 2017	852,491	$ 782	$ (123,051)	799,376	(51,453)	226,837
Balance, End of Period, Treasury Stock, shares (in shares) at Mar. 31, 2017			(2,946,000)
Balance Beginning of Period, Shares (in shares) at Dec. 31, 2016		77,666,000
Balance, Beginning of Period at Dec. 31, 2016	839,667	$ 777	$ (123,051)	798,652	(57,154)	220,443
Balance, Beginning of Period, Treasury Stock, shares (in shares) at Dec. 31, 2016			(2,946,000)
Net income	20,388
Balance End of Period, Shares (in shares) at Sep. 30, 2017		81,301,000
Balance, End of Period at Sep. 30, 2017	913,116	$ 813	$ (121,816)	817,071	(23,783)	240,831
Balance, End of Period, Treasury Stock, shares (in shares) at Sep. 30, 2017			(2,916,000)
Balance Beginning of Period, Shares (in shares) at Dec. 31, 2016		77,666,000
Balance, Beginning of Period at Dec. 31, 2016	839,667	$ 777	$ (123,051)	798,652	(57,154)	220,443
Balance, Beginning of Period, Treasury Stock, shares (in shares) at Dec. 31, 2016			(2,946,000)
Balance End of Period, Shares (in shares) at Dec. 31, 2017		81,306,000
Balance, End of Period at Dec. 31, 2017	$ 962,306	$ 813	$ (121,644)	821,758	(23,807)	285,186
Balance, End of Period, Treasury Stock, shares (in shares) at Dec. 31, 2017	(2,912,000)		(2,912,000)
Balance Beginning of Period, Shares (in shares) at Mar. 31, 2017		78,185,000
Balance, Beginning of Period at Mar. 31, 2017	$ 852,491	$ 782	$ (123,051)	799,376	(51,453)	226,837
Balance, Beginning of Period, Treasury Stock, shares (in shares) at Mar. 31, 2017			(2,946,000)
Net income	10,835					10,835
Other comprehensive income (loss), net of tax	17,295				17,295
Issuance of common stock for vesting of share based awards, net of shares withheld for taxes (in shares)		(498,000)	(25,000)
Issuance of common stock for vesting of share based awards, net of shares withheld for taxes	8,238	$ 5	$ 1,037	7,196
Share-based compensation	5,695			5,695
Exercise of warrants (in shares)		1,680,000
Exercise of warrants		$ 17		(17)
Balance End of Period, Shares (in shares) at Jun. 30, 2017		80,363,000
Balance, End of Period at Jun. 30, 2017	894,554	$ 804	$ (122,014)	812,250	(34,158)	237,672
Balance, End of Period, Treasury Stock, shares (in shares) at Jun. 30, 2017			(2,921,000)
Net income	3,159					3,159
Other comprehensive income (loss), net of tax	10,375				10,375
Issuance of common stock for vesting of share based awards, net of shares withheld for taxes (in shares)		(8,000)	(5,000)
Issuance of common stock for vesting of share based awards, net of shares withheld for taxes	(271)	$ 1	$ 198	(470)
Share-based compensation	5,301			5,301
Exercise of warrants (in shares)		946,000
Exercise of warrants	(2)	$ 8		(10)
Balance End of Period, Shares (in shares) at Sep. 30, 2017		81,301,000
Balance, End of Period at Sep. 30, 2017	913,116	$ 813	$ (121,816)	817,071	(23,783)	240,831
Balance, End of Period, Treasury Stock, shares (in shares) at Sep. 30, 2017			(2,916,000)
Balance Beginning of Period, Shares (in shares) at Dec. 31, 2017		81,306,000
Balance, Beginning of Period at Dec. 31, 2017	$ 962,306	$ 813	$ (121,644)	821,758	(23,807)	285,186
Balance, Beginning of Period, Treasury Stock, shares (in shares) at Dec. 31, 2017	(2,912,000)		(2,912,000)
Net income	$ 10,992					10,992
Other comprehensive income (loss), net of tax	21,612				22,144	(532)
Issuance of common stock (in shares)		297,000
Issuance of common stock	3,110	$ 3		3,107
Issuance of common stock through employee stock purchase plan (in shares)		0
Issuance of common stock through employee stock purchase plan	553			553
Issuance of common stock for vesting of share based awards, net of shares withheld for taxes (in shares)		(108,000)	(22,000)
Issuance of common stock for vesting of share based awards, net of shares withheld for taxes	(6,732)	$ 1	$ 910	(7,643)
Share-based compensation	4,745			4,745
Balance End of Period, Shares (in shares) at Mar. 31, 2018		81,711,000
Balance, End of Period at Mar. 31, 2018	998,440	$ 817	$ (120,734)	822,520	(1,663)	297,500
Balance, End of Period, Treasury Stock, shares (in shares) at Mar. 31, 2018			(2,890,000)
Balance Beginning of Period, Shares (in shares) at Dec. 31, 2017		81,306,000
Balance, Beginning of Period at Dec. 31, 2017	$ 962,306	$ 813	$ (121,644)	821,758	(23,807)	285,186
Balance, Beginning of Period, Treasury Stock, shares (in shares) at Dec. 31, 2017	(2,912,000)		(2,912,000)
Net income	$ 35,663
Other comprehensive income (loss), net of tax	(1,932)
Balance End of Period, Shares (in shares) at Sep. 30, 2018		88,016,000
Balance, End of Period at Sep. 30, 2018	$ 1,365,081	$ 880	$ (120,727)	1,187,963	(26,271)	323,236
Balance, End of Period, Treasury Stock, shares (in shares) at Sep. 30, 2018	(2,883,000)		(2,883,000)
Adoption of ASC 606 | Accounting Standards Update 2014-09	$ 1,854					1,854
Balance Beginning of Period, Shares (in shares) at Mar. 31, 2018		81,711,000
Balance, Beginning of Period at Mar. 31, 2018	998,440	$ 817	$ (120,734)	822,520	(1,663)	297,500
Balance, Beginning of Period, Treasury Stock, shares (in shares) at Mar. 31, 2018			(2,890,000)
Net income	11,376					11,376
Other comprehensive income (loss), net of tax	(22,578)				(23,643)	1,065
Issuance of common stock (in shares)		39,000
Issuance of common stock	65			65
Issuance of common stock for vesting of share based awards, net of shares withheld for taxes (in shares)		(16,000)
Issuance of common stock for vesting of share based awards, net of shares withheld for taxes	(467)		$ 2	(469)
Share-based compensation	5,471			5,471
Equity offering (in shares)		6,038,000
Equity offering	349,598	$ 60		349,538
Balance End of Period, Shares (in shares) at Jun. 30, 2018		87,772,000
Balance, End of Period at Jun. 30, 2018	1,341,905	$ 877	$ (120,732)	1,177,125	(25,306)	309,941
Balance, End of Period, Treasury Stock, shares (in shares) at Jun. 30, 2018			(2,890,000)
Net income	13,295					13,295
Other comprehensive income (loss), net of tax	(965)				(965)
Issuance of common stock (in shares)		261,000
Issuance of common stock	5,502	$ 3		5,499
Issuance of common stock for vesting of share based awards, net of shares withheld for taxes (in shares)		(17,000)	(7,000)
Issuance of common stock for vesting of share based awards, net of shares withheld for taxes	(215)		$ 5	(220)
Share-based compensation	5,559			5,559
Balance End of Period, Shares (in shares) at Sep. 30, 2018		88,016,000
Balance, End of Period at Sep. 30, 2018	$ 1,365,081	$ 880	$ (120,727)	$ 1,187,963	$ (26,271)	$ 323,236
Balance, End of Period, Treasury Stock, shares (in shares) at Sep. 30, 2018	(2,883,000)		(2,883,000)