Consolidated statements of changes in shareholders' equity - USD ($) $ in Thousands	Total	Common stock	Additional paid-in capital	Retained earnings	Accumulated other comprehensive income, net
Balance at Dec. 31, 2017	$ 596,729	$ 30,536	$ 418,596	$ 147,449	$ 148
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	41,819			41,819
Other comprehensive (loss) income, net of taxes	(7,613)				(7,613)
Stock based compensation expense	3,819	6	3,813
Restricted stock units vested and distributed, net of shares withheld	(2,555)	124	(2,679)
Shares issued under employee stock purchase program	669	17	652
Cash dividends declared	(1,909)			(1,909)
Balance at Jun. 30, 2018	630,959	30,683	420,382	187,250	(7,356)
Balance at Mar. 31, 2018	611,075	30,672	418,810	167,094	(5,501)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	22,065			22,065
Other comprehensive (loss) income, net of taxes	(1,855)				(1,855)
Stock based compensation expense	1,861	2	1,859
Restricted stock units vested and distributed, net of shares withheld	(278)	9	(287)
Cash dividends declared	(1,909)			(1,909)
Balance at Jun. 30, 2018	630,959	30,683	420,382	187,250	(7,356)
Balance at Dec. 31, 2018	671,857	30,725	424,146	221,213	(4,227)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	38,276			38,276
Other comprehensive (loss) income, net of taxes	13,396				13,396
Stock based compensation expense	3,785	6	3,779
Restricted stock units vested and distributed, net of shares withheld	(2,510)	124	(2,634)
Shares issued under employee stock purchase program	364	11	353
Cash dividends declared	(5,100)			(5,100)
Balance at Jun. 30, 2019	718,759	30,866	425,644	253,080	9,169
Balance at Mar. 31, 2019	694,577	30,853	423,647	236,947	3,130
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	18,688			18,688
Other comprehensive (loss) income, net of taxes	6,039				6,039
Stock based compensation expense	2,147	3	2,144
Restricted stock units vested and distributed, net of shares withheld	(137)	10	(147)
Cash dividends declared	(2,555)			(2,555)
Balance at Jun. 30, 2019	$ 718,759	$ 30,866	$ 425,644	$ 253,080	$ 9,169