Derivative Instruments and Hedging Activities - Impact of Interest Rate Swaps Designated As Hedging Instruments on the Company's Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of the period	$ 971,865
Balance at end of the period	949,046
Accumulated other comprehensive income for derivative instruments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of the period	0	$ 102
Unrealized loss on interest rate swaps	0	164
Balance at end of the period	$ 0	$ 266

Derivative Instruments and Hedging Activities - Impact of Interest Rate Swaps Designated As Hedging Instruments on the Company's Accumulated Other Comprehensive Income (Details) - USD ($)
$ in Thousands

3 Months Ended

Mar. 31, 2018

Mar. 31, 2017

AOCI Attributable to Parent, Net of Tax [Roll Forward]

Balance at beginning of the period

$ 971,865

Balance at end of the period

949,046

Accumulated other comprehensive income for derivative instruments

AOCI Attributable to Parent, Net of Tax [Roll Forward]

Balance at beginning of the period

$ 102

Unrealized loss on interest rate swaps

164

Balance at end of the period

$ 0

$ 266