Stock-Based Compensation Plans (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Weighted Average Grant Date Fair Value
Stock compensation expense (in dollars)		$ 3,717,000	$ 4,150,000	$ 3,509,000
The 2007 plan
Weighted Average Grant Date Fair Value
Balance at the beginning of the period (in dollars per share)		$ 17.98	$ 13.71	$ 13.71
Stock compensation expense (in dollars)		$ 3,681,000	$ 4,102,000	$ 3,459,000
Options cancelled (in shares)	155,745
Shares granted (in dollars per share)		$ 21.55	$ 18.53	$ 19.84
Shares cancelled (in dollars per share)		17.79		14.02
Shares vested (in dollars per share)		17.12	15.87	13.24
Balance at the end of the period (in dollars per share)	$ 20.24	$ 20.24	$ 17.98	$ 13.71
Aggregate Value
Balance at the beginning of the period (in dollars)		$ 7,131,200	$ 8,786,611	$ 7,060,474
Shares granted (in dollars)		2,944,941	2,713,159	4,710,362
Shares cancelled (in dollars)		(362,536)		(80,630)
Shares vested (in dollars)		(3,655,269)	(4,368,570)	(2,903,595)
Balance at the end of the period (in dollars)	$ 6,058,336	6,058,336	7,131,200	8,786,611
Employee Stock Purchase Plan
Weighted Average Grant Date Fair Value
Stock compensation expense (in dollars)		$ 36,000	$ 48,000	$ 50,000
Shares granted (in dollars per share)		$ 6.35	$ 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		11,014	10,374
Restricted stock | The 2007 plan
Unused Elements Abstract
Intrinsic value of unvested awards issued(in dollars)	$ 7,700,000	$ 7,700,000