Net Income Per Common Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	1 Months Ended	3 Months Ended		9 Months Ended
	Feb. 28, 2013	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Net Income Per Common Share [Line Items]
Weighted average number of diluted shares outstanding adjustment (in shares)		1,295,270	589,876	1,035,506	615,842
Adjustments to net income for purposes of computing income available to common stockholders		$ 0	$ 0	$ 0	$ 0
Stock compensation expense				16,092	6,564
3.375% Convertible Notes [Member]
Net Income Per Common Share [Line Items]
Potential shares issuable under net share settlement method (in shares)		286,205	0	128,594	0
Convertible Debt [Member] | 3.375% Convertible Notes [Member]
Net Income Per Common Share [Line Items]
Convertible notes stated interest rate		3.375%		3.375%
Conversion price (in dollars per share)		$ 28.31		$ 28.31
Term used to compute average closing price of stock for dilutive effect comparison		30 days		30 days
Stock Options [Member]
Net Income Per Common Share [Line Items]
Antidilutive securities excluded from computation of EPS		27,300	367,428	177,550	331,618
Options, granted (in shares)	130,600
Exercise period of stock options from date of grant				10 years
Exercise period of stock options from date of retirement				5 years
Restricted Stock Units (RSUs) [Member]
Net Income Per Common Share [Line Items]
Other than options, granted (in shares)	161,295
Performance Share Awards [Member]
Net Income Per Common Share [Line Items]
Other than options, granted (in shares)	135,055
Award vesting period				3 years
Minimum range of target award of stock plan				0.00%
Maximum range of target award of stock plan				250.00%
Equity Award Modification [Member]
Net Income Per Common Share [Line Items]
Stock compensation expense				$ 10,492