Stock-Based Compensation Plans (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Weighted Average Grant Date Fair Value
Stock compensation expense (in dollars)		$ 4,150,000	$ 3,509,000	$ 3,439,000
The 2007 plan
Weighted Average Grant Date Fair Value
Balance at the beginning of the period (in dollars per share)		$ 16.72	$ 13.71	$ 12.83
Stock compensation expense (in dollars)		$ 4,102,000	$ 3,459,000	$ 3,393,000
Options cancelled (in shares)	(135,368)
Shares granted (in dollars per share)		$ 18.53	$ 19.84	$ 14.25
Shares cancelled (in dollars per share)			14.02	12.41
Shares vested (in dollars per share)		15.87	13.24	12.01
Balance at the end of the period (in dollars per share)	$ 17.98	$ 17.98	$ 16.72	$ 13.71
Aggregate Value
Balance at the beginning of the period (in dollars)		$ 8,786,611	$ 7,060,474	$ 8,756,990
Shares granted (in dollars)		2,713,159	4,710,362	2,158,011
Shares cancelled (in dollars)			(80,630)	(745,876)
Shares vested (in dollars)		(4,367,983)	(2,903,595)	(3,108,651)
Balance at the end of the period (in dollars)	$ 7,131,787	7,131,787	8,786,611	7,060,474
Employee Stock Purchase Plan
Weighted Average Grant Date Fair Value
Stock compensation expense (in dollars)		$ 48,000	$ 50,000	$ 46,000
Shares granted (in dollars per share)		$ 6.17	$ 6.17	$ 3.19
Aggregate Value
Maximum percentage of cash compensation allowed to be deducted for the purchase of common stock by eligible employees		10.00%
Maximum number of shares to be purchased by employee in one calendar year		1,000
Maximum amount of shares to be purchased by employee in one calendar year (in dollars)		$ 25,000
Purchase price expressed as a percentage of the market price of the common stock on the purchase date or on the date of entry		85.00%
Shares issued		10,374	14,068
Restricted stock | The 2007 plan
Unused Elements Abstract
Intrinsic value of unvested awards issued(in dollars)	$ 8,000,000	$ 8,000,000