Stock-Based Compensation (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Stock-based compensation
Number of shares of common stock available for grant under the plan	2,000
Compensation expense related to the Plan	$ 6,807	$ 6,022	$ 6,908
Restricted Stock
Stock-based compensation
Period over which forfeiture and non-transferable restrictions lapse	4 years
Unrecognized compensation cost related to the restricted stock	11,787
Period over which unrecognized compensation cost is expected to be recognized	4 years
Shares
Balance at the beginning of the period (in shares)	864
Granted (in shares)	431	392	391
Vested (in shares)	(307)
Forfeited (in shares)	(8)
Balance at the end of the period (in shares)	980	864
Weighted Average Grant-Date Fair value
Balance at the beginning of the period (in dollars per share)	$ 16.81
Granted (in dollars per share)	$ 14.66
Vested (in dollars per share)	$ 18.55
Forfeited (in dollars per share)	$ 20.88
Balance at the end of the period (in dollars per share)	$ 15.28	$ 16.81
Intrinsic Value
Balance at the beginning of the period (in dollars)	14,517
Balance at the end of the period (in dollars)	$ 14,960	$ 14,517
2012 Plan
Stock-based compensation
Maximum term of options	3 years
Number of shares of common stock available for grant under the plan	1,998
Intrinsic Value
Number of shares allowed for issuance under the plan	2,000
2002 Plan
Stock-based compensation
Maximum term of options	10 years
Intrinsic Value
Number of shares allowed for issuance under the plan	4,200