Stock Compensation Plans - Performance-Based Restricted Stock Activity (Details) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Compensation expense
Total Compensation	$ 5,372	$ 4,871	$ 5,650
Restricted Stock, subject to performance criteria
Compensation expense
Total Compensation	1,318	$ 589	$ 2,479
Unamortized future compensation expense	$ 892
Summary of restricted stock activity
Outstanding shares	170
Shares vested	(25)
Shares awarded	171
Shares forfeited	(81)
Outstanding shares	236	170
Weighted average remaining term (years)
Outstanding (years)	1 year 10 months 6 days	1 year 8 months 16 days
Aggregate intrinsic value
Outstanding, beginning balance (in dollars)	$ 2,321
Shares vested (in dollars)	363
Shares awarded (in dollars)	2,573
Shares forfeited (in dollars)	1,190
Outstanding, Ending balance (in dollars)	$ 3,276	$ 2,321
Restricted Stock, subject to performance criteria | Three-year performance targets
Plan information
Performance period	3 years
Performance-based restricted stock, earned
Summary of restricted stock activity
Outstanding shares	34
Performance-based restricted stock, earned | Three-year performance targets
Plan information
Performance period	3 years
Vesting period (in years)	3 years
Performance-based restricted stock, unearned
Summary of restricted stock activity
Outstanding shares	202