Employee Benefits - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Contribution 401(k) Plan:
Defined contribution plan, employee minimum age requirement	21 years
Defined contribution plan, employer matching contribution, percent of employee's match	50.00%
Defined contribution plan, employer matching contribution, percent of employees' gross pay	6.00%
Defined contribution plan, company contributions during period	$ 2,400	$ 2,000	$ 1,500
Share-based Compensation:
Shares awarded during period (in shares)		1,000,000
Percentage of stock granted vested each year	20.00%
Benefit obligation	$ 5,200	$ 3,400
Service and interest costs	1,700	1,700	$ 1,700
Benefit obligation, fair value	$ 11,500	$ 11,400
Assumptions used calculating benefit obligation, discount rate	3.84%	4.05%
Restricted Stock
Share-based Compensation:
Number of shares granted (in shares)	284,948	318,197	9,599
2006 Incentive Plan
Share-based Compensation:
Maximum number of shares authorized (in shares)	5,000,000
Maximum term after which no award will be exercisable (in years)	10 years
Number of shares available for grant (in shares)	1,851,866
Share based compensation expense	$ 4,600	$ 3,500	$ 1,500
Tax benefit form options expenses during period	353	170	366
Total unrecognized compensation cost related to nonvested share-based compensation arrangements	$ 9,600
Total unrecognized compensation cost related to nonvested share-based compensation arrangements, period for recognition	2 years
Total fair value of shares vested during period	$ 800	300	400
2006 Incentive Plan | Restricted Stock
Share-based Compensation:
Maximum number of shares authorized (in shares)	1,000,000
Number of shares available for grant (in shares)	6,546
Share based compensation expense	$ 120	115	85
Total fair value of shares vested during period	$ 2,200	$ 897	$ 998
Shares awarded during period (in shares)	5,494	18,197	9,599
Number of shares granted (in shares)	279,454	300,000
Price of the stock granted (in dollars per share)	$ 23.43	$ 17.87