Share-Based Compensation (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 08, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense recognized	$ 4,817	$ 4,394	$ 6,380
Unrecognized Compensation Cost	$ 3,060
Expiration date of 2007 Stock Incentive Plan	May 20, 2024
Outstanding:
Beginning Balance (in shares)		77,000
Beginning Balance, weighted average exercise price (in dollars per share)		$ 16.29
Granted (in shares)	0	0	0
Granted, weighted average exercise price (in dollars per share)	$ 0	$ 0	$ 0
Stock options exercised (in shares)		77,334	27,619
Exercised, weighted average exercise price (in dollars per share)			$ 0
Ending Balance (in shares)			77,000
Ending balance, weighted average exercise price (in dollars per share)			$ 16.29
Exercisable (in shares)
Stock price per share (in dollars per share)				$ 24.70
Intrinsic value under share based compensation scheme		$ 20	$ 85
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense recognized	$ 4,603	$ 4,231	$ 6,263
Unrecognized Compensation Cost	$ 3,060
Weighted Average Remaining Amortization Periods (in years)	9 months 18 days
Exercisable (in shares)
Expected to vest	904,000	986,000	1,004,000
Outstanding:
Balance (in shares)	986,000	1,004,000	1,028,000
Granted (in shares)	252,000	304,000	353,000
Vested (in shares)	(334,000)	(322,000)	(155,000)
Cancelled or forfeited (in shares)	0	0	(222,000)
Balance (in shares)	904,000	986,000	1,004,000
Beginning balance, Weighted average grant-date fair value (in dollars per share)	$ 13.34	$ 12.74	$ 13.24
Granted, Weighted average grant-date fair value (in dollars per share)	18.90	15.52	11.35
Vested, Weighted average grant-date fair value (in dollars per share)	13.67	13.54	12.27
Forfeitures, Weighted average grant date fair value	0	0	13.19
Ending balance, Weighted average grant-date fair value (in dollars per share)	$ 14.77	$ 13.34	$ 12.74
Phantom Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense recognized	$ 214	$ 163	$ 117
Unrecognized Compensation Cost	$ 0
Weighted Average Remaining Amortization Periods (in years)	0 years
Outstanding:
Balance (in shares)	157,000	145,000	132,000
Granted (in shares)	10,000	10,000	10,000
Dividend equivalents issued	3,000	2,000	3,000
Redeemed for common stock (in shares)	0	0	0
Balance (in shares)	170,000	157,000	145,000
Granted, Weighted average grant-date fair value (in dollars per share)	$ 21.35	$ 16.25	$ 11.71
Performance Vested Restricted Stock Units [Member] | Scheduled to Vest January 1, 2019 [Member]
Exercisable (in shares)
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Not Expected To Vest Outstanding Number	0
Expected to vest	213,000
Outstanding:
Balance (in shares)	213,000
Performance Vested Restricted Stock Units [Member] | Scheduled to Vest January 1, 2020 [Member]
Exercisable (in shares)
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Not Expected To Vest Outstanding Number	0
Expected to vest	167,000
Outstanding:
Balance (in shares)	167,000
Performance Vested Restricted Stock Units [Member] | Scheduled to Vest January 1, 2021 [Member]
Exercisable (in shares)
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Not Expected To Vest Outstanding Number	0
Expected to vest	141,000
Outstanding:
Balance (in shares)	141,000
2007 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of shares authorized under restricted stock, unrestricted stock, RSU's and stock options to officers, employees and non-employee directors (in shares)	6,500,000
Exercisable (in shares)
Available for future grants (in shares)	2,894,000