Stock-Based Compensation (Details 2) (USD $) In Thousands, except Share data, unless otherwise specified	1 Months Ended	12 Months Ended			1 Months Ended		12 Months Ended	1 Months Ended	12 Months Ended
	Oct. 31, 2012 Employment agreement	Dec. 31, 2012 Restricted stock units	Dec. 31, 2011 Restricted stock units	Dec. 31, 2010 Restricted stock units	Nov. 30, 2008 Restricted stock units granted in 2008	Jul. 31, 2008 Restricted stock units granted in 2008	Dec. 31, 2012 Restricted stock units granted in 2008	Oct. 31, 2012 Restricted stock units granted in 2012	Dec. 31, 2012 Restricted stock units granted in 2012
Stock-Based Compensation
Restricted stock units awarded (in shares)	30,529	222,425			5,000	750,000		191,895
Vesting rights on each of the tenth, eleventh and twelfth year anniversaries of the grant date							one-third
Vesting rights on each of the tenth, eleventh and twelfth year anniversaries of the grant date (as a percent)							33.00%		33.00%
Number of years from grant date for first one-third vesting							10 years		1 year
Number of years from grant date for second one-third vesting							11 years		2 years
Number of years from grant date for third one-third vesting							12 years		3 years
Nonvested Shares
Nonvested at the beginning of the period (in shares)		669,000	755,000
Issued (in shares)	30,529	222,425			5,000	750,000		191,895
Vested (in shares)		(154,800)	(68,400)
Forfeited (in shares)		(13,200)	(17,600)
Nonvested at the end of the period (in shares)		723,425	669,000	755,000
Weighted Average Grant-Date Fair Value
Nonvested at the beginning of the period (in dollars per share)		$ 18.27	$ 18.26
Nonvested at the end of the period (in dollars per share)		$ 19.78	$ 18.27	$ 18.26
Recognized stock-based compensation expense		$ 1,858	$ 2,206	$ 2,065
Unrecognized stock-based compensation costs		$ 9,065	$ 6,062	$ 7,863
Weighted average remaining recognition period of unrecognized stock-based compensation costs		4 years	6 years 8 months 12 days	6 years 10 months 24 days