Operations and Summary of Significant Accounting Policies - Stock Repurchase Program (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accelerated Share Repurchases [Line Items]
Repurchase of common stock (in shares)		1,338,894
Repurchase of common stock		$ 47,144,000	$ 2,981,000	$ 9,825,000
Stock repurchase, average cost per share (in USD per share)	$ 36.27	$ 35.21
Treasury Stock
Accelerated Share Repurchases [Line Items]
Repurchase of common stock		$ 47,144,000	$ 2,981,000	$ 9,825,000
2015 Stock Repurchase Program
Accelerated Share Repurchases [Line Items]
Common stock repurchase, authorized amount		$ 50,000,000.0
Stock repurchase program expiration date	Dec. 31, 2015
Settlement of accelerated share repurchase program	$ (25,000,000)
Repurchase of common stock (in shares)		689,184